Simultaneous expression of CD4 and CD8 antigens by a substantial proportion of resting porcine T lymphocytes

CTLA4Ig-induced linked regulation of allogeneic T cell responses

The mechanisms by which CTLA4Ig exerts its powerful immunomodulatory effects are not clear. We show here that CTLA4Ig can induce linked regulation of allogeneic porcine T cell responses in vitro. Naive miniature swine SLA(dd) T cells were rendered hyporesponsive to specific allogeneic Ag after coculturing with MHC-mismatched SLA(cc) stimulators in the presence of CTLA4Ig. These Ag-specific hyporesponsive T cells were subsequently able to actively inhibit the allogeneic responses of naive syngeneic T cells in an MHC-linked fashion, as the responses of naive SLA(dd) responders against specific SLA(cc) and (SLA(ac))F(1) stimulators were inhibited, but allogeneic responses against a 1:1 mixture of SLA(aa) (I(a), II(a)) and SLA(cc) (I(c), II(c)) were maintained. This inhibition could be generated against either class I or class II Ags, was radiosensitive, and required cell-cell contact. Furthermore, the mechanism of inhibition was not dependent upon a deletional, apoptotic pathway, but it was reversed by anti-IL-10 mAb. These data suggest that CTLA4Ig-induced inhibition of naive allogeneic T cell responses can be mediated through the generation of regulatory T cells via an IL-10-dependent mechanism.

Lymphocyte subsets in porcine tonsillar crypt epithelium

The palatine tonsils are part of the mucosa-associated lymphoid tissue (MALT), strategically located in the oropharynx at the entrance of respiratory and gastrointestinal tracts, and are recognized portals of entry and sites of multiplication and persistence of several pathogens in pigs. As the tonsillar crypt epithelium is in close contact with external environment and the underlying lymphoid tissue, the characterization of the intra-epithelial lymphocyte subpopulations is essential for the understanding of initial steps of pathogenesis of several diseases. In this work we investigated specific lymphocyte subsets in the tonsillar crypt epithelium of 10 adult healthy pigs, using monoclonal antibodies against lymphocyte markers CD3, CD4, CD8, gammadelta T cell receptor and immunoglobulin light-chain in an avidin-biotin immunoperoxidase technique. The crypt epithelium was usually extensively infiltrated by a diverse population of T cells and by B cells. The degree of infiltration of each subset was variable among animals and within individual animals. In the T cell population CD4 cells and gammadelta TCR cells predominated over CD8 cells. These data suggest that the crypt lymphoepithelium is capable of participating in both cellular and humoral immune responses and that gammadelta T cells may play an important role in the defense of this mucosa.

Phenotypic analysis of peripheral CD4+ CD8+ T cells in the rat

Among peripheral T cells, the expression of CD4 and CD8 is almost mutually exclusive. However, here we show, using flow cytometric analysis, that ex vivo approximately 6% of rat T cells stained for both CD4 and CD8. These double positive cells were also detected by confocal microscopy. Only around 50% of double positive cells expressed the CD8beta chain, the remaining cells expressed the CD8alpha chain alone. Double positive cells were blast-like with a phenotype, distinct from that of either CD4 or CD8 single positive cells, suggestive of an activated state. Previous reports of double positive T cells have also suggested that coexpression of CD4 and CD8 is linked to the activation state of the cell. There was an indication that priming animals with a hapten-carrier complex increased the ratio of CD8alphaalpha : alphabeta expressing double positive T cells, although we did not detect an increase in the frequency of double positive T cells following priming. We also show that the frequency of double positive cells was reduced following thymectomy and with age. In conclusion, these studies show that peripheral T cells expressing both CD4 and CD8 can be detected in the rat and that they are phenotypically distinct from CD4 and CD8 single positive T cells.

Evidence for a parapox ovis virus-associated superantigen

As shown in a number of species, susceptibility to infectious diseases can be efficiently reduced following application of inactivated parapox ovis viruses (iPPOV). However, the basic mechanism for this stimulating capacity of iPPOV remains unclear. When analyzed, the interaction of iPPOV with porcine peripheral blood mononuclear cells was seen to involve T helper cells as the main target cell population responding to iPPOV. These cells displayed a strong proliferation, and were the major source for the observed increased levels of IL-2. Activation of the T helper cells was MHC class II dependent, but not MHC class II restricted: cellular processing of iPPOV was not required for presentation by autologous, allogeneic or xenogeneic MHC class II molecules. Furthermore, CD3 and CD4 molecules were involved in the stimulation, indicating a receptor-mediated activation of T helper cells. The results demonstrated typical characteristics of a superantigen-induced response providing evidence for a viral component within PPOV functioning as superantigen(s) in swine.

Interspecies major histocompatibility complex-restricted Th cell epitope on foot-and-mouth disease virus capsid protein VP4

T-cell epitopes within viral polypeptide VP4 of the capsid protein of foot-and-mouth disease virus were analyzed using 15-mer peptides and peripheral blood mononuclear cells (PBMC) from vaccinated outbred pigs. An immunodominant region between VP4 residues 16 and 35 was identified, with peptide residues 20 to 34 (VP4-0) and 21 to 35 (VP4-5) particularly immunostimulatory for PBMC from all of the vaccinated pigs. CD25 upregulation on peptide-stimulated CD4(+) CD8(+) cells-dominated by Th memory cells in the pig-and inhibition using anti-major histocompatibility complex class II monoclonal antibodies indicated recognition by Th lymphocytes. VP4-0 immunogenicity was retained in a tandem peptide with the VP1 residue 137 to 156 sequential B-cell epitope. This B-cell site also retained immunogenicity, but evidence is presented that specific antibody induction in vitro required both this and the T-cell site. Heterotypic recognition of the residue 20 to 35 region was also noted. Consequently, the VP4 residue 20 to 35 region is a promiscuous, immunodominant and heterotypic T-cell antigenic site for pigs that is capable of providing help for a B-cell epitope when in tandem, thus extending the possible immunogenic repertoire of peptide vaccines.

Extrathymic CD4/CD8 double positive T cells

Mature T lymphocytes expressing the alphabeta T cell receptor are generally classified as either CD4+ or CD8+, based on the mutually exclusive expression of these two lymphocyte coreceptors. Contrary to this conventional division, there is considerable evidence that significant numbers of CD4/CD8 double positive (DP) lymphocytes exist in the peripheral blood and secondary lymphoid tissues of swine, chickens and monkeys. Although CD4/CD8 DP T cells are rarely present in human peripheral blood the relative percentage of this lymphocyte population can increase spontaneously in healthy individuals and in persons suffering from certain disease conditions. DP can also be found among those T cells infiltrating arthritic joints, rejected kidney grafts and certain tumors. In humans, and rats, CD4/CD8 DP T cells appear transiently following activation of their progenitors. Murine DP cells have been described as a subset of intraepithelial lymphocytes (IELs). However, the relationship of IELs to DP cells in the peripheral blood of other species is unknown. Because of their unconventional phenotype and rarity in human and mice, most immunologists have ignored extrathymic CD4/CD8 DP lymphocytes. Nevertheless, their abundance in the peripheral blood of swine, monkeys and chickens makes it impossible to dismiss this lymphocyte population. Here are reports that have described extrathymic lymphocytes exhibiting a CD4+CD8dim phenotype in several species reviewed. Swine and monkey lymphocytes with this phenotype are represented by small resting cells that simultaneously express CD4 and CD8alpha molecules. The available evidence favors the notion that such DP T cells in swine are comprised predominantly of MHC class II restricted memory CD4+ helper T cells that after activation have acquired the ability to express the CD8alpha chain and then to maintain this DP phenotype. Moreover, porcine CD4/CD8 DP T cells appear to be comprised of memory cells due to their ability to respond to recall antigen, resilience to thymectomy, increase in proportion with age, expression of memory T cell markers, production of interferon-gamma and localization to inflammatory sites. Some of these characteristics are also descriptive of human and monkey CD4/CD8 DP T cells. Thus, in swine, humans and monkeys, these phenotypically distinct lymphocytes appear to represent a primed T cell subset. The possible functional significance of the simultaneous expression of the CD4 and CD8 co-receptors on mature T cells is discussed.

Mutations abrogating the RNase activity in glycoprotein E(rns) of the pestivirus classical swine fever virus lead to virus attenuation

Classical swine fever (CSF) is a severe hemorrhagic disease of swine caused by the pestivirus CSF virus (CSFV). Amino acid exchanges or deletions introduced by site-directed mutagenesis into the putative active site of the RNase residing in the glycoprotein E(rns) of CSFV abolished the enzymatic activity of this protein, as demonstrated with an RNase test suitable for detection of the enzymatic activity in crude cell extracts. Incorporation of the altered sequences into an infectious CSFV clone resulted in recovery of viable viruses upon RNA transfection, except for a variant displaying a deletion of the histidine codon at position 297 of the long open reading frame. These RNase-negative virus mutants displayed growth characteristics in tissue culture that were undistinguishable from wild-type virus and were stable for at least seven passages. In contrast to animals inoculated with an RNase-positive control virus, infection of piglets with an RNase-negative mutant containing a deletion of the histidine codon 346 of the open reading frame did not lead to CSF. Neither fever nor extended viremia could be detected. Animals infected with this mutant did not show decrease of peripheral B cells, a characteristic feature of CSF in swine. Animal experiments with four other mutants with either exchanges of codons 297 or 346 or double exchanges of both codons 297 and 346 showed that all these RNase-negative mutants were attenuated. All viruses with mutations affecting codon 346 were completely apathogenic, whereas those containing only changes of codon 297 consistently induced clinical symptoms for several days, followed by sudden recovery. Analyses of reisolated viruses gave no indication for the presence of revertants in the infected animals.

Cellular immune responses of pigs induced by vaccination with either a whole cell sonicate or pepsin-digested Brachyspira (Serpulina) hyodysenteriae bacterin

Brachyspira (Serpulina) hyodysenteriae infection of pigs (swine dysentery) causes a mucohemorrhagic diarrhea resulting in significant economic losses for producers. A commercial vaccine consisting of a proteinase-digested bacterin has shown efficacy in the reduction of disease due to B. hyodysenteriae. Vaccines consisting of whole cell bacterins, however, generally fail to protect pigs from disease. In the present study, cellular immune responses induced by a proteinase-digested bacterin were compared to responses induced by a whole cell sonicate antigen preparation. In addition, usage of either squalene or Freund's incomplete adjuvants in combination with each antigen preparation was also compared. Both antigen preparations induced significant cellular immune responses as measured by in vitro (IFN-gamma production and T cell proliferation) and in vivo methods (DTH responses). No significant differences were detected in proliferative, interferon-gamma (IFN-gamma), or delayed type hypersensitivity (DTH) responses by pigs receiving either adjuvant or antigen preparation. T cells (CD3(+)) but not B cells from vaccinated animals proliferated in response to in vitro stimulation with B. hyodysenteriae antigen. CD8(+) (single positive and CD4/CD8 double positive) and gammadelta(+) T cells were particularly responsive. In addition, high percentages of both CD8 single positive and CD4/CD8 double positive cells were detected in antigen-stimulated cultures. These findings demonstrate the unique sensitivity of porcine CD8(+) T cells to priming for recall response by vaccination with a proteinase-digested B. hyodysenteriae bacterin.

Respiratory mucosal immunization with reovirus serotype 1/L stimulates virus-specific humoral and cellular immune responses, including double-positive (CD4(+)/CD8(+)) T cells

Respiratory virus infections are a serious health challenge. A number of models that examine the nature of the respiratory immune response to particular pathogens exist. However, many pathogens that stimulate specific immunity in the lung are frequently not effective immunogens at other mucosal sites. A pathogen that is an effective respiratory as well as gastrointestinal immunogen would allow studies of the interaction between the mucosal sites. Reovirus (respiratory enteric orphan virus) serotype 1 is known to be an effective gut mucosal immunogen and provides a potential model for the relationship between the respiratory and the gut mucosal immune systems. In this study, we demonstrate that intratracheal immunization with reovirus 1/Lang (1/L) in C3H mice resulted in high titers of virus in the respiratory tract-associated lymphoid tissue (RALT). High levels of reovirus-specific immunoglobulin A were determined in the RALT fragment cultures. The major responding components of the bronchus-associated lymphoid tissue were the CD8(+) T lymphocytes. Cells from draining lymph nodes also exhibited lysis of reovirus-infected target cells after an in vitro culture. The present study also describes the distribution of transiently present CD4(+)/CD8(+) double-positive (DP) T cells in the mediastinal and tracheobronchial lymph nodes of RALT. CD4(+)/CD8(+) DP lymphocytes were able to proliferate in response to stimulation with viral antigen in culture. Furthermore, these cells exhibited lysis of reovirus-infected target cells after in vitro culture. These results establish reovirus 1/L as a viable model for future investigation of the mucosal immune response in the RALT and its relationship to the common mucosal immune system.

Quantification of B, T and null lymphocyte subpopulations in the blood and lymphoid organs of the pig

Research on the pig's immune system is not only of general biological interest; the pig is also becoming more important as a large animal model in human biomedical research, e.g. as a donor for xeno-transplantation. With the increasing panel of monoclonal antibodies against porcine lymphocyte markers it is possible to gain more insight into the distribution and phenotype of lymphocyte subpopulations in the pig. In this study we investigated B cells (surface IgG: sIgG, sIgM and sIgA) and T cells (CD2, CD4, CD8, 8/1, MAC320) in the peripheral blood (pBL), thymus, spleen, tonsil, mesenteric and inguinal lymph nodes (mLN, iLN), jejunal and ileal Peyer's patches (jejPP, ilPP) in Göttingen minipigs. A flow cytometric technique was employed which enabled three color indirect immunofluorescence. B cell stained for surface IgG and surface IgA were found only in small percentages. Surface IgM positive cells were distributed at higher rates, with up to 24.9% in the iLN. Up to 64.2% of CD4+ and up to 73.1% of CD8+ cells were observed in the thymus. Most of the CD4+ cells were CD4/CD8 double positive cells. These cells were mostly triple positive in combination with CD2. A larger fraction of CD2- were CD8- which are taken to be NK cells. MAC320, a marker for a subtype of gamma/delta T cells, was predominantly found on cells in the pBL. The standardized flow cytometric technique produced comparable data on the distribution of major lymphocyte subpopulations in the blood and different lymphoid organs of the pig. The results provide a basis for future studies using the pig as animal model.

Characterization of porcine T lymphocytes and their immune response against viral antigens

T lymphocytes play a central role in the antigen-specific immune response against various pathogens. To detect and to characterize porcine T lymphocytes, monoclonal antibodies (mAb) against leukocyte differentiation antigens had been raised and classified for their specificity. Analyses of porcine T lymphocytes with specific mAb against CD4 and CD8 differentiation antigens revealed differences in the composition of the porcine T-lymphocyte population compared to other species. In addition to the known subpopulations, CD4+CD8- T helper cells and CD4-CD8+ cytolytic T lymphocytes, extra-thymic CD4+CD8+ T lymphocytes and a substantial proportion of CD2-CD4-CD8- T cell receptor (TcR)-gamma delta+ T cells could be detected in swine. Functional analyses of porcine T-lymphocyte subpopulations revealed the existence of two T-helper cell fractions with the phenotype CD4+CD8- and CD4+CD8+. Both were reactive in primary immune responses in vitro, whereas only cells derived from the CD4+CD8+ T-helper-cell subpopulation were able to respond to recall antigen in a secondary immune response. With regard to T lymphocytes with cytolytic activities, two subsets within the CD4-CD8+ T-cell subpopulation could be defined by the expression of CD6 differentiation antigens: CD6- cells which showed spontaneous cytolytic activity and CD6+ MHC I-restricted cytolytic T lymphocytes including virus-specific cytolytic T lymphocytes. These results enable now a detailed view into the porcine T-cell population and the reactivity of specific T cells involved in the porcine immune response against pathogens. Furthermore this knowledge offers the possibility to investigate specific interactions of porcine T lymphocytes with virus-specific epitopes during vaccination and viral infections.

Molecular Cloning and Characterization of a Novel CD1 Gene from the Pig

Much effort is underway to define the immunological functions of the CD1 multigene family, which encodes a separate lineage of Ag presentation molecules capable of presenting lipid and glycolipid Ags. To identify porcine CD1 homologues, a cosmid library was constructed and screened with a degenerate CD1 α3 domain probe. One porcine CD1 gene (pCD1.1) was isolated and fully characterized. The pCD1.1 gene is organized similarly to MHC class I and other CD1 genes and contains an open reading frame of 1020 bp encoding 339 amino acids. Expression of pCD1.1 mRNA was observed in CD3− thymocytes, B lymphocytes, and tissue macrophages and dendritic cells. The pCD1.1 cDNA was transfected into Chinese hamster ovary cells, and subsequent FACS analysis demonstrated that mAb 76-7-4, previously suggested to be a pig CD1 mAb, recognizes cell surface pCD1.1. Structurally, the pCD1.1 α1 and α2 domains are relatively dissimilar to those of other CD1 molecules, whereas the α3 domain is conserved. Overall, pCD1.1 bears the highest similarity with human CD1a, and the ectodomain sequences characteristically encode a hydrophobic Ag-binding pocket. Distinct from other CD1 molecules, pCD1.1 contains a putative serine phosphorylation motif similar to that found in human, pig, and mouse MHC class Ia molecules and to that found in rodent, but not human, MHC class-I related (MR1) cytoplasmic tail sequences. Thus, pCD1.1 encodes a molecule with a conventional CD1 ectodomain and an MHC class I-like cytoplasmic tail. The unique features of pCD1.1 provoke intriguing questions about the immunologic functions of CD1 and the evolution of Ag presentation gene families.

Effects of SIVmac infection on peripheral blood CD4+CD8+ T lymphocytes in cynomolgus macaques

We have previously reported that CD4+CD8+ double-positive (DP) T cells with a resting memory phenotype exist in a substantial proportion of peripheral blood lymphocytes of adult cynomolgus macaques. In this study, we examined the effects of simian immunodeficiency virus of macaque (SIVmac) infection on DP T cells. In vitro, SIVmac239 nef-open (239) and its nef-deletion mutant replicated well in both CD4+CD8- and DP T cells. However, when the macaques were infected with 239, DP, but not CD4+CD8-, T cells were transiently increased in parallel with cell activation and viral replication, followed by depletion within 1 month postinfection. Interestingly, the nef gene was required for depletion but not for the increase and activation of DP T cells. These data suggest that the pathogenic SIV infection may downmodulate production and/or blood circulation of DP T cells by a Nef function-related mechanism(s) different from that for the depletion of CD4+CD8- T cells.

T-cell populations in the pig intestinal lamina propria: memory cells with unusual phenotypic characteristics

We have previously presented evidence of a highly organized and compartmentalized structure of the small intestinal lamina propria of the pig. In this study, we conducted a detailed analysis of the T-cell populations found at this site, and compared these T cells with cell populations found in other tissue sites and the periphery. We showed that the CD4+ and CD8+ T-cell populations found in the pig gut are of memory phenotype, defined by CD45 isoform expression, but show few signs of recent activation. They show a high degree of phenotypic and therefore presumably functional homogeneity. Both CD4- and CD8-positive cells show strong parallels in the patterns of surface molecule expression, suggesting similar pressures on differentiation. The unique combination of surface molecules found on lamina propria T cells is found only infrequently on cells in other lymphoid sites.

Chicken CD4, CD8alphabeta, and CD8alphaalpha T cell co-receptor molecules

New knowledge has recently been obtained about the evolutionary conservation of CD4, CD8alphaalpha, and CD8alphabeta T cell receptor (TCR) co-receptor molecules between chicken and mammals. This conservation extends from biochemical structure and tissue distribution to function. Panels of monoclonal antibodies and polyclonal antisera against different epitopes of chicken CD8 and CD4 molecules have proven their value in several recent studies. Chicken CD8 allotypes and homozygous strains carrying these allotypes have been established and these strains provide excellent models for further studies. The extensive polymorphism of CD8alpha in chickens has not been observed in any other species, suggesting that CD8alpha and CD8beta have evolved under different selective pressure in the chicken. A large peripheral blood CD4+CD8+ T cell population in chicken resembles that observed in some human individuals but the inheritance of peripheral blood CD4CD8alphaalpha T cells in the chicken is a unique observation, which suggests the presence of a single gene responsible for CD8alpha, but not CD8beta, specific expression. Despite these unique findings in chicken, the data on CD4, CD8alphaalpha, and CD8alphabeta molecules show that they have evolved before the divergence of mammalian and avian branches from their reptilian ancestors.

Vaccine-induced, pseudorabies virus-specific, extrathymic CD4+CD8+ memory T-helper cells in swine

Pseudorabies virus (PRV; suid herpesvirus 1) infection causes heavy economic losses in the pig industry. Therefore, vaccination with live attenuated viruses is practiced in many countries. This vaccination was demonstrated to induce extrathymic virus-specific memory CD4+CD8+ T lymphocytes. Due to their major histocompatibility complex (MHC) class II-restricted proliferation, it is generally believed that these T lymphocytes function as memory T-helper cells. To directly prove this hypothesis, 15-amino-acid, overlapping peptides of the viral glycoprotein gC were used for screening in proliferation assays with peripheral blood mononuclear cells of vaccinated d/d haplotype inbred pigs. In these experiments, two naturally processed T-cell epitopes (T1 and T2) which are MHC class II restricted were identified. It was shown that extrathymic CD4+CD8+ T cells are the T-lymphocyte subpopulation that responds to epitope T2. In addition, we were able to show that cytokine secretion can be induced in these T cells through recall with inactivated PRV and demonstrated that activated PRV-primed CD4+CD8+ T cells are able to induce PRV-specific immunoglobulin synthesis by PRV-primed, resting B cells. Taken together, these results demonstrate that the glycoprotein gC takes part in the priming of humoral anti-PRV memory responses. The experiments identified the first T-cell epitopes so far known to induce the generation of virus-specific CD4+CD8+ memory T lymphocytes and showed that CD4+CD8+ T cells are memory T-helper cells. Therefore, this study describes the generation of virus-specific CD4+CD8+ T cells, which is observed during vaccination, as a part of the potent humoral anti-PRV memory response induced by the vaccine.

Differential adhesion molecule expression on porcine mononuclear cell populations

Adhesion molecule expression was analysed on porcine blood and lymphoid organ CD4+ CD8 naive T helper (Th) lymphocytes, CD4+CD8+ memory Th lymphocytes (particular to the pig), CD4-CD8high cytotoxic T (Tc) lymphocytes, CD4 CD8low NK cells (CD3- in the pig), CD4-CD8- T-cell receptor-gammadelta-positive (TCRgammadelta+) lymphocytes, B lymphocytes and monocytes. While CD44 expression was relatively homogeneous amongst mononuclear cells, differences were noted for the integrins. Blood naive Th lymphocytes were CD49d(low)CD11a(low), as were splenic naive Th cells; blood memory Th lymphocytes were CD49d(high)CD11a(low), splenic memory Th cells were CD49d(high)CD11a(high) with a CD49d(high)CD11a(low) subpopulation; blood Tc lymphocytes were mainly CD49d(low)CD11a(low), and splenic cells were CD49d(high) CD11a(high). Lymph node lymphocytes were more homogeneous in their integrin expression. These were relatively CD49d(low)CD11a(low), except the memory Th lymphocytes which had higher integrin expression. B lymphocytes related to the majority of integrin(low) T cells, while monocytes and NK cells were CD49d(high) CD11a(high); gammadelta T lymphocytes showed variable CD49d expression but a CD11a(high) phenotype. CD49d(high) CD11a(high) co-expression was found, and this phenotype was typical of, but not exclusive to, CD25+ (activated) lymphocytes. These results demonstrated that porcine memory Th lymphocytes and NK cells, as well as activated cells, would have increased integrin-dependent activities compared with naive Th lymphocytes, and integrin-dependent reactions would probably vary between blood and lymphoid organ cells.

Report on the analyses of mAb reactive with porcine CD8 for the second international swine CD workshop

Based on an analysis of their reactivity with porcine peripheral blood lymphocytes (PBL), only three of the 57 mAbs assigned to the T cell/activation marker group were grouped into cluster T9 along with the two wCD8 workshop standard mAbs 76-2-11 (CD8a) and 11/295/33 (CD8b). Their placement was verified through the use of two-color cytofluorometry which established that all three mAbs (STH101, #090; UCP1H12-2, #139; and PG164A, #051) bind exclusively to CD8+ cells. Moreover, like the CD8 standard mAbs, these three mAbs reacted with two proteins with a MW of 33 and 35 kDa from lymphocyte lysates and were, thus, given the wCD8 designation. Because the mAb STH101 inhibited the binding of mAb 76-2-11 but not of 11/295/33, it was given the wCD8a designation. The reactivity of the other two new mAbs in the T9 cluster with the various subsets of CD8+ lymphocytes were distinct from that of the other members in this cluster including the standards. Although the characteristic porcine CD8 staining pattern consisting of CD8low and CD8high cells was obtained with the mAb UCP1H12-2, a wider gap between the fluorescence intensity of the CD8low and CD8high lymphocytes was observed. In contrast, the mAb PG164A, not only exclusively reacted with CD4-/CD8high lymphocytes, but it also failed to recognize CD4/CD8 double positive lymphocytes. It was concluded that this mAb is specific for a previously unrecognized CD8 epitope, and was, thus, given the wCD8c designation. A very similar reactivity pattern to that of PG164A was observed for two other mAbs (STH106, #094; and SwNL554.1, #009). Although these two mAbs were not originally positioned in the T cell subgroup because of their reactivity and their ability to inhibit the binding of PG164A, they were given the wCD8c designation. Overall, five new wCD8 mAbs were identified. Although the molecular basis for the differences in PBL recognition by these mAbs is not yet understood, they will be important in defining the role of CD8+ lymphocyte subsets in health and disease.

Early changes in the phenotypic composition of lymphocytes in the bronchoalveolar lavage of pigs after aerogenic immunization with Pasteurella multocida aerosols

The phenotypic composition of bronchoalveolar lymphocytes (BALL) of healthy untreated pigs and of pigs immunized via aerosol with a live Pasteurella multocida mutant was measured cytofluorometrically in comparison to blood lymphocytes (PBL). Cells were analyzed using monoclonal antibodies against porcine IgM, IgA, IgG and SWC3 in single-colour fluorescence and the following antibody combinations for two-colour fluorescence: CD2/SWC1, SWC1/CD25 and CD4/CD8. In nonimmunized pigs, differences between lymphocyte subsets derived from blood and lung were obvious. The numbers of CD2-SWC1+ T-cells, CD25+ activated lymphocytes and IgG+ cells were significantly higher in the bronchoalveolar compartment. Aerosol immunization with P. multocida caused only insignificant changes in the phenotypic composition of PBL whereas the composition of lung-derived lymphocytes changed markedly. The percentage of CD2-SWC1+ lymphocytes and of CD25+ cells coexpressing the SWC1 antigen in BALL increased up to 10 days after aerosol administration, whereas the percentage of all Ig+ cells decreased. These data reflect an early cellular reaction to an aerogenic immunization with a P. multocida aerosol, characterized by an increase in CD2+ T-cells and a T-cell activation.

A novel peripheral CD4+ CD8+ T cell population: inheritance of CD8alpha expression on CD4+ T cells

In this study we show the inheritance of a CD4+ CD8+ peripheral Tcell population in the H.B15 chicken strain. A large proportion of alphabeta T cells in peripheral blood (20-40%), spleen (10-20%) and intestinal epithelium (5-10%) coexpress CD4 and CD8alpha, but not CD8beta. CD4+ CD8alpha alpha cells are functionally normal T cells, since they proliferate in response to mitogens and signals delivered via the alphabeta T cell receptor as well as via the CD28 co-receptor. These cells induce in vivo a graft versus host-reaction, providing further evidence for their function as CD4+ T cells. The CD4+ CD8alpha alpha T cell population was found in 75% of the first progeny and in 100% of further progenies, demonstrating that coexpression of CD4 and CD8 on peripheral T cells is an inherited phenomenon. In addition, cross-breeding data suggest a dominant Mendelian form of inheritance. The hereditary expression of CD8alpha on peripheral CD4+ T cells in chicken provides a unique model in which to study the regulation of CD4 and CD8 expression.

Cooperation between transmissible gastroenteritis coronavirus (TGEV) structural proteins in the in vitro induction of virus-specific antibodies

Following infection of haplotype defined NIH-miniswine with virulent transmissible gastroenteritis coronavirus (TGEV), isolated mesenteric lymph node CD4+ T-cells mounted a specific proliferative response against infectious or inactivated purified virus in secondary in vitro stimulation. A specific, dose-dependent response to the three major recombinant viral proteins: spike (S), membrane (M), and nucleoprotein (N), purified by affinity chromatography, was characterized. Induction of in vitro antibody synthesis was analyzed. The purified recombinant viral proteins induced the in vitro synthesis of neutralizing TGEV-specific antibodies when porcine TGEV-immune cells were stimulated with each of the combinations made with two of the major structural proteins: S + N, S + M, and to a minor extent with M + N, but not by the individual proteins. S-protein was dissociated from purified virus using NP-40 detergent and then micellar S-protein oligomers (S-rosettes) were formed by removing the detergent. These occurred preferentially by the association of more than 10 S-protein trimmers. These S-rosettes in collaboration with either N or M-proteins elicited TGEV-specific antibodies with titers up to 84 and 60%, respectively, of those induced by the whole virus. N-protein could be partially substituted by a 15-mer peptide that represents a T helper epitope previously identified in N-protein (Antón et al. (1995)). These results indicate that the induction of high levels of TGEV-specific antibodies requires stimulation by at least two viral proteins, and that optimum responses are induced by a combination of S-rosettes and the nucleoprotein.

Immunophenotypic characterization of tumor infiltrating lymphocytes and peripheral blood lymphocytes isolated from melanomatous and non-melanomatous Sinclair miniature swine

Selectively-bred Sinclair miniature swine exhibit a high incidence of congenital malignant melanoma which either proves fatal (10-15% of tumor-bearing piglets) or spontaneously regresses with a biphasic immunological phenomenon (85-90%) and no recurrence of malignancy. Mononuclear leukocytes were isolated from cutaneous melanomas and peripheral blood specimens collected from melanomatous (tumor-bearing) Sinclair swine during second-phase regression, and from peripheral blood specimens collected from non-melanomatous (tumor-free) Sinclair swine and control Hanford swine. Leukocyte identities were determined with single- and dual-parameter indirect immunofluorescence assays via flow cytometry. Assays for the specific surface antigens CD45, CD2, CD4, CD8, CD1, MHC class II, and N1 were employed to develop immunophenotypic profiles within the gated lymphocyte clusters from each TIL and PBL suspension. Significantly more CD8+ T-lymphocytes were identified in TIL suspensions than in peripheral blood leukocyte (PBL) suspensions (P < and = 0.05), regardless of breed or tumor status. Conversely, PBL suspensions contained significantly higher percentages of CD4+ T-lymphocytes than the levels found in TIL suspensions (P < and = 0.05). Virtually all TIL were MHC class II+, whereas the percentages of PBL expressing this antigen were markedly lower (P < and = 0.05). The percentages of T-lymphocytes co-expressing CD4 and CD8, a normal subset unique to swine, were generally consistent in all TIL and PBL suspensions examined. The results of this study have firmly established the immunophenotypic identities of cells associated with the second-phase regression phenomenon of this melanoma and have identified specific variations in the leukocyte profiles of the respective TIL and PBL suspensions.

Research applications using pigs

The pig is an excellent research model for numerous human conditions and diseases. As a consequence, valuable information has been generated that has direct applications for human medicine. Research with an applied or agriculture-based emphasis also is essential to commercial pork production. Information must be exchanged between researchers using the pig as a biomedical model and investigators conducting applied research. The numerous research applications using the pig illustrate that the pig is a valuable resource for both biomedical and applied research.

Phenotypic classification of porcine lymphocyte subpopulations in blood and lymphoid tissues

The pig is a useful model for the heterogeneity of the mammalian immune system and has also recently received attention as a possible source of organs for human transplantation. Here we report a detailed analysis of porcine lymphocyte phenotypes. Peripheral blood alpha beta T cells consisted of four subsets (CD4+8-, CD4+8lo, CD4-8lo and CD4-8hi) and gamma delta T cells of three (CD2-4-8-, CD2+4-8lo and CD2+4-8-). There were in addition, a large proportion of non-T-non-B lymphocytes with CD2+3-4-8lo surface immunoglobulin-negative phenotype containing natural killer (NK) activity. A striking observation was the relatively low frequency of alpha beta T cells in the blood of young pigs. Similar phenotypes were also identified in the cells from peripheral lymphoid tissues, though the proportions of the gamma delta T cells and the non-T-non-B lymphocytes in the lymph nodes and tonsil were much lower and the majority of the gamma delta T cells in the lymphoid tissues bore CD2 and or CD8. In thymus, the small thymocytes were predominantly CD3-4+8+ while the mature large thymocytes displayed phenotypes similar to those of peripheral T cells. Thus this work has directly defined porcine alpha beta and gamma delta T cells demonstrated the T-cell nature of the unique CD4+8+ subset of peripheral lymphocytes, revealed the high heterogeneity of the CD8+ cells, and established the phenotype of NK cells. The functional properties of these defined porcine lymphocyte subsets can now be experimentally determined in health and disease.

Preparation of monoclonal anti-porcine CD3 antibodies and preliminary characterization of porcine T lymphocytes

The CD3-T-cell receptor complex is the clonotypic surface structure by which T lymphocytes recognize foreign antigens and are subsequently activated. Because of the low immunogenicity of the CD3 molecules, anti-CD3 monoclonal antibodies (mAb) are difficult to prepare and have not been available in several species. Following isolation of porcine CD3, 14 anti-porcine CD3 mAb were prepared, which define six groups of CD3-epsilon epitopes, coprecipitate two types of TCR and reveal considerable heterogeneity of CD3 expression amongst lymphocyte subpopulations. Thus, both CD3 positive and negative subpopulations of CD2 or CD8 positive cells were found in the blood. The density of CD3 on CD2+ or CD8+ cells was relatively low and heterogeneous, whereas the CD2-, CD8- or MAC320+ T cells expressed CD3 at a higher and more homogeneous level. Finally, in the thymus, staining with anti-CD3 resolved large thymocytes into two subsets: one expressing a high level of CD3 and the other being negative. In contrast, small thymocytes expressed CD3 at a low and more homogeneous level. Immunohistological studies confirmed the presence of clearly detectable CD3 in thymus medulla and the T-cell regions of peripheral lymphoid tissues. Most of the mAb were mitogenic, when presented to peripheral blood mononuclear cells in immobilized form. The anti-CD3 mAb also induced redirected cytotoxicity which was shown to be Fc receptor dependent.

Differential binding of two monoclonal antibodies directed against the chicken CD8 alpha molecule

Two murine monoclonal antibodies (mAb), CT8 and AV14, have been shown to recognise the avian homologue of the mammalian CD8 alpha molecule. In previous flow cytometry studies we could discriminate two subpopulations of CD8+ T cells, expressing either a high level (CD8Bright+) or a low level (CD8Dim+) of CD8 molecules. The staining patterns of mAb AV14 and mAb CT8 were not always identical for individual chickens. In this study the discrepancy in the reactivity of these mAb was examined, using outbred White Leghorn chickens as well as (B14B14)-MHC inbred Wellcome chickens. The results show that mAb AV14 and mAb CT8 recognise different epitopes on the chicken CD8 alpha molecule. The CD8Bright+ cells appeared to express the CD8 alpha beta heterodimer and the CD8Dim+ cells the CD8 alpha alpha homodimer. Conformational differences between the alpha beta heterodimer and the alpha alpha homodimer could account for the differences in binding characteristics found for the two mAb. The existence of a polymorphism of the CD8 alpha molecule in outbred White Leghorn chickens was suggested by the failure of peripheral blood leucocytes from some chickens to react with mAb AV14. This heterogeneity was not observed in the Wellcome line.

Differentiation between MHC-restricted and non-MHC-restricted porcine cytolytic T lymphocytes

The immune system of swine is unique in that the expression of CD4 and CD8 antigens defines four subpopulations of resting extrathymic T lymphocytes. Beyond phenotypic differences to other species, porcine T lymphocytes, particularly when derived from infected animals, are known to show high non-specific cytolytic in vitro activity. Here we describe the putative porcine CD6 antigen (workshop CD6; wCD6) which enables a phenotypic separation of T lymphocytes responsible for major histocompatibility complex (MHC)-restricted and non-MHC-restricted cytotoxicity. The putative porcine CD6 analogue, wCD6, a protein with a molecular mass of 110,000, shows high specificity for T lymphocytes and is neither expressed on B lymphocytes nor on cells of the myeloid lineage. In the extrathymic T-lymphocyte compartment wCD6 characterizes two T-lymphocyte fractions: wCD6+ T lymphocytes including both CD4+ T-helper cell subpopulations (CD4+CD8- and CD4+CD8+) and within the CD4-CD8+ fraction cells with high CD8 antigen density. In contrast the CD4-CD8- gamma/delta T-cell receptor (TCR) subset and CD4-CD8+ cells with low CD8 antigen density are included in the wCD6- T-lymphocyte fraction. Functional studies with separated wCD6 fractions revealed that the wCD6- cells can be characterized by spontaneous and non-MHC restricted cytolytic activity, whereas the wCD6+ T lymphocytes are responsible for MHC-restricted T-cell functions. Thus, the porcine wCD6 is an important antigen to discriminate between MHC-restricted and non-MHC-restricted cytotoxicity.

Occurrence of T lymphocytes in perivascular regions of the lung after intratracheal infection of swine with Pasteurella multocida

The defence mechanisms of the lung acting against airborne antigens (bacteria) are not yet fully understood. Therefore, we investigated cell-derived immunological processes in porcine pulmonary tissue. The incidence and distribution of leukocyte subpopulations in lungs, lung lymph nodes and tonsils from eight animals intratracheally infected with Pasteurella multocida (P.m.) type A wild strain and from four non-infected control animals were established by immunohistochemistry, using a panel of monoclonal antibodies (mAbs) against specific porcine leukocyte antigens: MHC Class II (MHC II), SWC1, SWC3a, CD2a, CD4a, CD8b. In the test animals, a broad layer of SWC1+ cells and SWC3a+ cells emerged in the subsinusoidal region of lung lymph nodes and in the bronchoalveolar spaces of the lung as early as 4 and 24 h after infection, and in the subsinusoidal regions of the lung lymph nodes only very few cells could be stained with the mAb against the MHC II antigen. We could not detect any MHC Class II+ cells in the bronchoalveolar spaces at this time of the investigation. In the course of the disappearance of the SWC1+ cells and SWC3+ cells, CD2a+, CD4a+ and, in lower numbers, CD8b+ T lymphocytes seemed to concentrate in the perivascular and, partially, the peribronchial regions of the lung 72 h after infection. By means of the double immunostaining method, we could demonstrate an accumulation of CD4a+ cells and CD8b+ cells after infection which lacked the SWC1 antigen, indicating that these cells were activated T lymphocytes. The same cell types (SWC1-/CD4a+ and SWC1-/CD8b+ cells) as well as CD8b-/CD4a+ cells could be observed in the interstitium of the lung 72 h after infection.

Lymphocyte transendothelial migration toward smooth muscle cells in interleukin-1 beta-stimulated co-cultures is related to fibronectin interactions with alpha 4 beta 1 and alpha 5 beta 1 integrins

We previously reported infiltration of immune-inflammatory cells in coronary arteries from cardiac allografts, associated with increased endothelial and smooth muscle cell fibronectin synthesis regulated by interleukin (IL)-1 beta. We now investigate, using a porcine endothelial-smooth muscle cell co-culture system, whether IL-1 beta-stimulated fibronectin production is functionally important in lymphocyte transendothelial migration. Lymphocytes were harvested from porcine peripheral blood and, in the unactivated state or following activation with phorbol myristic acetate (PMA) and IL-2, were characterized by fluorescence-activated cell sorter (FACS) analysis and added to a confluent endothelial monolayer on the upper chamber of a transwell system. Endothelial cells, as well as smooth muscle cells (in the bottom of the chamber), were stimulated with IL-1 beta. Then transendothelial lymphocyte migration was determined in the presence of CS1 and RGD (fibronectin) peptides, blocking alpha 4 beta 1 and alpha 5 beta 1 integrin receptors on lymphocyte surfaces, respectively. A 55-70% inhibition of lymphocyte migration was observed when compared to control peptides. The combination of CS1 and RGD peptides did not significantly enhance the inhibitory effect of either peptide alone. A similar decrease in lymphocyte transendothelial migration toward smooth muscle cells was documented using a monoclonal antibody to cellular fibronectin. Furthermore, using smooth muscle cell conditioned medium, we reproduced the enhanced transendothelial lymphocyte migration as well as the inhibition with blocking peptides or fibronectin antibodies. Our data suggest that cytokine-mediated fibronectin synthesis in vascular cells recruits inflammatory cells through interactions of specific peptides with cell surface alpha 4 beta 1 and alpha 5 beta 1 integrins.

Cellular immune responses of pigs after primary inoculation with porcine respiratory coronavirus or transmissible gastroenteritis virus and challenge with transmissible gastroenteritis virus

The contribution of cell-mediated immunity to protective immunity against virulent transmissible gastroenteritis virus (TGEV) infection conferred by primary porcine respiratory coronavirus (PRCV) or TGEV exposure was assessed in pigs that were challenged with TGEV 24 days after a primary oronasal inoculation with PRCV or TGEV when 11 days old. PRCV exposure induced partial protection against TGEV challenge in suckling pigs based upon a decreased number of diarrhea cases (42% vs. 90% in age-matched control pigs), limited virus shedding in feces, and increases in virus-neutralizing serum antibody titers; in contrast, all 11-day-old pigs inoculated with TGEV were completely protected after challenge. Weaned pigs were also studied to eliminate any possibility that lactogenic immunity from contact PRCV-exposed sows contributed to protection against TGEV. Once weaned, none of the PRCV-exposed or age-matched control pigs had diarrhea after TGEV challenge; moreover, both groups exhibited less rectal virus shedding than suckling pigs. Vigorous lymphocyte proliferative responses (> 96,000 counts per minute (cpm)) were detected in mononuclear cells prepared from mesenteric (MLN) and bronchial (BLN) lymph nodes of TGEV-primed pigs. Analyses of these responses indicate that virus-specific cell-mediated immune responses correlated with protection against rectal and nasal virus shedding after TGEV challenge. Primary inoculation of 11-day-old pigs with PRCV induced moderate, transient virus-specific lymphocyte proliferation (> 47,000 cpm) in MLN from both suckling and weaned pigs after TGEV challenge. Substantial BLN proliferative responses (> 80,000 cpm) correlated with failure to detect TGEV in nasal secretions from these pigs. Virus-specific lymphocyte proliferation in spleens was delayed in onset and of lower magnitude than that observed in MLN and BLN. Virulent TGEV exposure resulted in increased percentages of T cell subsets, especially in the lamina propria and MLN, mucosa-associated lymphoid tissues in proximity to the primary replication site of TGEV in the small intestine. Our results confirm that PRCV infection primes anti-viral immune responses and, thus, contributes to partial immunity against virulent TGEV challenge.

Swine model of Haemophilus ducreyi infection

Haemophilus ducreyi is a strict human pathogen that causes sexually transmitted genital ulcer disease. We infected domestic swine with H. ducreyi 35000, resulting in the development of cutaneous ulcers histologically resembling human chancroid lesions. Intraepidermal lesions progressed from pustules to ulcers containing polymorphonuclear leukocytes and were accompanied by a dermal inflammatory infiltrate containing T cells and macrophages. H. ducreyi was recovered from lesions up to 17 days after inoculation, and pigs did not develop immunity to reinfection with the challenge strain. Features of the model include inoculation through abrasions in the epidermis, ambient housing temperatures for infected pigs, the ability to deliver multiple different inocula to a single host, and the availability of monoclonal antibodies against porcine immune cells permitting immunohistochemical characterization of the host immune response to H. ducreyi infection.

More newly formed T than B lymphocytes leave the intestinal mucosa via lymphatics

Many lymphocytes are produced in the intestinal mucosa, especially in the Peyer's patches. These newly formed lymphoid cells leave the gut wall, undergo further maturation and many reach the lamina propria of the intestinal mucosa where they function as effector and regulator cells of the intestinal immune response. However, the number and subset composition of these newly formed lymphocytes emigrating from the gut wall are not known. Therefore, the intestinal lymph duct was cannulated in eight minipigs, in which the mesenteric lymph nodes had been removed 3 months earlier. Thus, it was possible to obtain all lymphocytes leaving the intestinal mucosa including the Peyer's patches via lymphatics. The hourly output of lymphocyte subsets was examined over the course of 93 h. The percentage and the absolute numbers of newly formed T cells (CD2+, CD8+) and B cells (IgA+, IgM+) were determined by examining the incorporation of the DNA precursor bromodeoxyuridine. After a single i.v. bromodeoxyuridine injection 8.5% of the T, 55% of the IgA+ and 25% of the IgM+ cells were labeled. In absolute numbers (1.9 +/- 0.7) x 10(6) newly formed T cells, (0.4 +/- 0.3) x 10(6) IgA+ cells and (0.5 +/- 0.4) x 10(6) IgM+ cells emigrated from the gut wall per hour. Both T and B lymphocyte subpopulations that are produced in the intestinal mucosa leave the gut wall via lymphatics; interesting, the T cells outnumber the B cells. Obviously the induction and maintenance of mucosal immunity depend to a large extent on the function of newly formed T lymphocytes emigrating from the Peyer's patches and/or from the mucosa without Peyer's patches.

Lymphoid and non-lymphoid cells in the epithelium and lamina propria of intestinal mucosa of pigs

The jejunum and ileum of 5 day old and adult normal pigs and of 45 day old germ free pigs were used to study the lymphocyte pools in the epithelium and lamina propria by sequential treatments with EDTA, four hours, and 12 hours of collagenase treatment. In adult animals the incubation of the jejunal wall with EDTA resulted in mean (SD) 26.8 (10.9) x 10(6) intraepithelial lymphocytes per g of tissue. The ileal wall gave lower cell yields. After complete digestion of the lamina propria by collagenase a further yield of 35.2 (10.2) x 10(6)/g lymphocytes was achieved. The separation of the gut wall from 5 day old pigs resulted in a 10-fold lower total lymphocyte yield, and the tissue was totally digested after four hours of collagenase treatment. Many eosinophils and mast cells were found in the suspensions from adult animal tissues after the collagenase treatment; 4.7 x 10(6)/g and 4.8 x 10(6)/g, respectively. The suspensions after 12 hour collagenase incubation contained up to 30% plasma cells. Almost all cells isolated by EDTA incubation were CD8+ T cells. After collagenase incubation CD4+ and CD8+ T lymphocytes were found in all animal groups, and in adult animals up to 20% surface Ig+ cells were harvested. When the incorporation of the thymidine analogue bromodesoxyuridine was used to study the lymphocyte production in vivo 3 to 7% lymphocytes in the epithelium were labelled 24 hours later (lamina propria T lymphocytes about 1%). In this study lymphoid as well as non-lymphoid cells have been analysed in mucosal cell suspensions. The absolute cell yield per gram of mucosal tissue is a basis to estimate the pool sizes of intraepithelial and lamina propria lymphocytes.

Porcine T-cell receptors: molecular and biochemical characterization

Two subclasses of CD3 associated T-cell receptors (TcR) have been described so far, consisting of either an alpha and beta chain (TcR alpha beta) or a gamma and delta chain (TcR gamma delta). Of the two subclasses, the TcR alpha beta is the one predominantly expressed on peripheral T lymphocytes of humans and rodents. TcR gamma delta T lymphocytes represent only a minor subset in these species. Among all mammalian species studied so far, swine showed the most diversified composition of the T-lymphocyte population characterized by the expression of CD4 and CD8 differentiation antigens. Besides CD4+CD8- and CD4-CD8+ T lymphocytes, CD4+CD8+ and CD4-CD8- T lymphocytes are prominent in the extrathymic T-lymphocyte compartment. Because of the lack of specific monoclonal antibodies (mAb), to date the porcine TcR can only be characterized with biochemical and molecular biological methods. TcR on porcine peripheral blood T lymphocytes with the phenotype CD4+ and/or CD8+ are characterized as 46-48 kDaR heterodimers which were supposed to represent the porcine TcR alpha beta. Biochemical analyses of the CD4-CD8- T lymphocytes revealed three distinct TcR gamma delta; all are characterized by a 40 kDa delta chain but differed in their gamma chains. One gamma chain with a molecular mass of 38 kDaR is preferentially expressed on CD4-CD8- T lymphocytes derived from peripheral blood; another chain with molecular mass of 37 kDaR is evenly distributed between CD4-CD8- T lymphocytes from blood and lymphoid tissues.(ABSTRACT TRUNCATED AT 250 WORDS)

Characteristics of porcine T lymphocytes and T-cell lines

Monoclonal antibodies (mAb) against leucocyte differentiation antigens have altered the way in which immunologists examine the immune system. These mAb allow us to identify distinct surface molecules on leucocyte populations, by which these cells can be classified, isolated and studied for their functional properties. This review summarizes the knowledge about differentiation antigens useful in the characterization of porcine T lymphocytes. Furthermore, it focuses on several properties of porcine T lymphocytes, T-lymphocyte subpopulations and the generation of porcine antigen-specific T-cell lines.

Analyses of mAb reactive with porcine CD8

Among all mAb submitted to the first porcine CD workshop, based on FCM analyses six mAb could be identified to recognize the porcine CD8 analogue (workshop Nos. 004, 051, 052, 053, 108 and 109). In immunoprecipitation studies three mAb (Nos. 004, 108 and 109) recognized an antigen with an apparent molecular mass of about 35 kDa under reducing conditions and about 70 kDa under non-reducing conditions. The molecular masses of the antigens recognized by the three other mAb (Nos. 051, 052 and 053) are still unknown. Epitope analyses performed by blocking experiments led to the determination of two CD8 epitopes: CD8a and CD8b. CD8a is recognized by mAb Nos. 004, 051 and 052, and CD8b by Nos. 053, 108 and 109.

Porcine peripheral blood CD4+/CD8+ dual expressing T-cells

The porcine T-cell population is unique in that there is a large percentage of CD+CD8+ dual expressing peripheral T-cells. This paper reviews the data available on these porcine T-cells and compares them to the much rarer dual expressing T-cells in humans. The percent of dual expressing cells increases with activation in in vitro culture with various antigens including pseudorabies virus. The percent of resting dual expressing cells also increases with the age of the pig. Flow-cytometric-sorted dual expressing cells responded in culture to the super antigen staphylococcal enterotoxin B. Selected CD4+CD8- cells cultured in vitro developed expression of CD8 and maintained the dual expressing phenotype for the 12 weeks of culture. Dual expressing cells freshly prepared from porcine blood did not express the IL-2 receptor as demonstrated by their failure to bind FITC-IL-2 and an anti-porcine IL-2 receptor monoclonal antibody. In response to activation with phorbol myristic acetate, CD4, but not CD8, was down regulated on the dual expressing T-cells. In summary, porcine dual expressing T-cells constitute a substantial percentage of the porcine peripheral T-cell pool. These cells appear to contain the majority of the memory T-cell with their frequency increasing with blood donor age and in vitro culture. Although the receptor specificity is not known, they have a functional receptor. Finally, the function of the two accessory molecules CD4 and CD8 in these cells is not known, but their regulation is distinct, thereby suggesting no equivalent roles in immune function.

Analyses of monoclonal antibodies reactive with porcine CD6

Amongst the monoclonal antibodies (mAbs) submitted to the first porcine CD workshop, two mAbs (workshop numbers 055 and 120) could be identified to recognize the porcine CD6 analogue. Both mAbs seemed to be highly T-cell specific and showed neither reactivity with cells of the myeloic lineage nor with B lymphocytes. The observed molecular mass of the antigen precipitated by mAb 120 of 110 kDa confirmed this classification. Without molecular analyses of the antigen recognized by mAb 055, but similar staining pattern in FCM compared with 120, mAb 055 was allocated to the wCD6 subcluster.

Studies on the distribution of immune cells in the uteri of prepubertal and cycling gilts

To establish the cellular basis for the local immune response in the porcine uterus, immunohistochemical studies using a panel of monoclonal antibodies to pig leukocytes were conducted on uterine tissues from prepubertal and cycling gilts. In prepubertal uteri, neutrophils were the most predominant cell type, while MHC class II+ cells and CD2+ T lymphocytes were also common. At the early-stage of the oestrous cycle, CD2+ T cells were numerous in the endometrium, particularly in the uterine epithelium and subepithelial regions. However, by the mid-stage of the cycle there was a significant and dramatic fall in CD2+ T cells and other lymphocytes expressing the CD4, CD8 and CD1 phenotypes, MHC class II+ cells were predominant throughout the endometrium. During late oestrus there was a dramatic infiltration of neutrophils into the subepithelial stroma. A distinct increase in the CD2+ intraepithelial T lymphocyte population was also observed at this stage of the cycle. It was concluded that in the healthy, non-pregnant pig uterus T lymphocytes, macrophages and neutrophils were the prominent leukocyte cell types and their migration and distribution in the uterus was strongly influenced by the oestrous cycle. These immune cells may play an important interactive role in the cyclic cellular changes in both the structure and function of the endometrium. Furthermore, the leukocyte phenotypes found in the porcine endometrium indicate that a local cellular immune response could be elicited.

Inflammatory response in the pig uterus induced by seminal plasma

The immunological and physiological influence of seminal plasma on the local uterine environment was investigated by immunohistochemical and flow cytometrical studies on uterine tissues and lymph nodes taken from gilts after mating with a vasectomised boar and from control, unmated gilts. These studies revealed that mating with a vasectomised boar induces an acute transient inflammatory response in the endometrium resulting in marked changes in the presence and distribution of leukocytes and extensive proliferation of the endometrial glands. At the same time there was an increase in CD8L and sIg+ cells and an up-regulation of MHC class II and IL-2 receptor expression in the uterine lymph nodes of mated pigs. This would suggest that seminal plasma deposited in the uterus can activate cells in the local draining lymph nodes. Together, these results demonstrate in utero that pronounced immunological and physiological changes are induced in vivo by seminal plasma.

Distribution of lymphocyte subpopulations in thymus, spleen, and peripheral blood of specific pathogen free pigs from 1 to 40 weeks of age

Using flow-microfluorometry analysis and cluster determinant (CD) markers, we studied how lymphocyte subpopulations in lymphoid organs of specific-pathogen-free pigs developed in pigs from birth to young adulthood. Cell suspensions of the thymus and spleen were prepared and peripheral blood cells were collected at 1, 4, 10, and 40 weeks of age. Tissue sections of the thymus and spleen were stained with monoclonal antibodies directed against CD2 and immunoglobulin to localize the CD2-Ig- lymphocyte subpopulation. In the thymus, only limited changes were observed in the lymphocyte subpopulations with time. Most thymocytes expressed CD4 or CD8 or both. Most CD2-Ig- cells or, 'null cells', (5-13%) were observed in the medulla of the thymus and probably represented a recirculating cell type. In the spleen and blood the percentage of CD2+ and Ig+ cells increased significantly with time, the former increasing from about 30-60% owing to an increase of CD8+ cells. Therefore, the selective increase of the CD8+ population also caused the CD4/CD8 ratio to change. Although CD2+ cells in the spleen and blood are positive for CD4 or CD8, but not for both, quantities of CD4+ CD8+ cells were also observed. Half of the lymphocytes in the spleen and blood were typed as null cells at 1 week of age and decreased in proportion to the increase of the CD8+ and Ig+ cells. Nevertheless, quantities of null cells were still present in the spleen blood at 40 weeks of age. Almost all these were located in the red pulp of the spleen. This study indicates an effect of age and housing conditions on the distribution of the lymphocyte subpopulations, and especially on the CD8+ subset. Quantities of CD4+CD8+ cells as well as CD4-CD8- were observed in blood, but also in spleen of pigs. The function of high numbers of null cells directly after birth are discussed.

Major histocompatibility antigen class II expressing resting porcine T lymphocytes are potent antigen-presenting cells in mixed leukocyte culture

The immune system of swine is unique in that the expression of CD4 and CD8 antigens defines four subpopulations of extrathymic resting T lymphocytes in blood as well as in lymphoid tissues. Recently, we documented an additional peculiarity of the porcine T lymphocyte population: a substantial proportion of resting T lymphocytes show constitutive surface expression of MHC II antigens (Saalmüller et al. 1991, Immunobiol. 183, 102). These cells belong predominantly either to the CD4-CD8+ or to the CD4+CD8+ T lymphocyte subpopulations. This report describes the antigen-presenting cell function of MHC II+ T lymphocytes in mixed leukocyte cultures. Experiments employing highly purified T lymphocytes as alloantigen-presenting stimulator cells resulted in a high proliferative and cytolytic alloantigen-specific T lymphocyte response. After separation of T lymphocyte stimulators into MHC II- and MHC II+ fractions, alloantigen-presenting cell function could be assigned to the MHC II+ T lymphocyte subset. Although the mechanisms involved in the response to alloantigen are not completely understood and may be different from conventional antigen presentation, this is the first report where naive resting MHC II+CD8+ T lymphocytes can be defined as antigen-presenting cells, presenting alloantigen to cells of their own lineage.

Isolation and characterization of gamma delta T lymphocyte cell lines from Sinclair swine peripheral blood

Sinclair miniature swine represent a breed of miniature swine which display a significant incidence of inheritable melanoma which undergo a developmentally regulated spontaneous regression. In an attempt to characterize the host cellular immune response to the melanoma, lymphocyte cell lines have been generated from peripheral blood and designated as peripheral blood lymphocyte cell lines (PBLCLs). The cell lines were expanded in vitro without the addition of exogenous mediators, cloned by limiting dilution, and characterized by flow microfluorimetry, Western, and Northern blot analysis. The cell lines were shown to be CD2-, CD4-, CD8-, and slg-, a phenotype consistent with a null cell population described in swine. The null cell population in swine has been reported to consist of a subpopulation of cells which express the gamma delta T cell receptor (TCR) heterodimer, swine gamma delta T lymphocytes. The PBLCLs were further analyzed by flow microfluorimetry and observed to express the IL-2R, swine MHC Class II antigens, and the endothelial lymphocyte adhesion marker (CD44), which can function as a homing receptor for the skin. In addition, the PBLCLs were observed to express the antigen which is recognized by mAb 86D, an antibody that has been reported to recognize an external epitope on a subset of gamma delta TCR bearing swine T lymphocytes. Western blot analysis of Triton X-114 phase fractions of a PBLCL revealed a protein recognized by the W6 antibody, an antibody which recognizes a conserved region of the C delta chain. Furthermore, Southern and Northern blot analysis indicated that the PBLCL have rearranged the TCR gamma chain gene and express mRNA from the TCR gamma and delta chain genes prior to and following treatment with ionomycin or Concanavalin A. Therefore, the data indicates that the PBLCLs represent swine gamma delta T lymphocyte cell lines which should enable us to enhance our understanding of the role of gamma delta T lymphocytes in the porcine immune system.

Expression of gamma/delta T cell receptors in porcine thymus

Swine possess an extraordinarily high number of T lymphocytes with the phenotype CD4-CD8- in peripheral blood as well as in lymphoid tissues. This subpopulation is subdivided into at least four subsets defined by the expression of CD2 and three biochemically distinct gamma/delta T cell receptors. The four subsets differ largely in their pattern of lymphoid homing in that CD2- subsets, historically referred to as null lymphocytes, predominate in the circulating pool, whereas CD2+ subsets are enriched in lymphoid tissues. Here we document the expression of all three types of gamma/delta T cell receptors by CD4-CD8- porcine thymocytes, which provides the first evidence for a thymic origination of all subsets of porcine gamma/delta T lymphocytes. The biochemical analysis shows that three distinct gamma-chains form disulfide-bonded cell surface heterodimers with a common delta-chain and that glycosylation of all chains is already completed within the thymus. Surprisingly, CD2- subsets, which are known to be enriched among thymic emigrants and which numerically predominate in peripheral blood, are underrepresented in the thymus, suggesting a high export rate.

Lymphoid cells in afferent and efferent intestinal lymph: lymphocyte subpopulations and cell migration

Gut wall emigrating cells have been characterized in the intestinal lymph. The intestinal lymph duct was cannulated in 6-month-old minipigs. Under non-restraining conditions the efferent lymph from the mesenteric lymph nodes was collected in seven normal animals. Lymph coming directly from the gut (afferent lymph) was also collected in 18 pigs after resection of the mesenteric lymph node chains 3 months previously. The intestinal lymph flow was similar in both groups (around 18 ml/h). The lymphoid cell yield was 1.2 +/- 1.0 x 10(6)/h in control animals, while in mesenteric lymph node resected pigs it was around 20 times higher (26.2 +/- 17.6 x 10(6)/h). In the gut-derived lymph 76.5 +/- 8.8% T lymphocytes were observed (CD4+, 48.1 +/- 15.5%; CD8+, 53.6 +/- 12.7%). The percentage of immunoglobulin-positive cells was lower (IgM+, 10.1 +/- 4.5; IgA+, 1.7 +/- 1.1). In 14 mesenteric lymph node resected pigs a mean of 5.6 +/- 3.1 x 10(8) lymphocytes from the gut lymph were labelled in vitro with a fluorescent dye and retransfused. The labelling index of fluorescent cells in the intestinal lymph increased rapidly and remained at a high level until 44 h after cell transfusion. A four-to-ten times lower labelling index was found in the spleen, various lymph nodes and Peyer's patches. Most of the recovered lymphocytes were T cells. This model provides access to the cell pool leaving the gut wall, thus allowing an examination of its role in the gastrointestinal tract and other mucosal-lined organs.

Molecular cloning of porcine T cell receptor alpha, beta, gamma and delta chains using polymerase chain reaction fragments of the constant regions

Fragments of the constant regions of porcine alpha, beta, delta and two types of gamma T cell receptor (TcR) chains were obtained by reverse transcription and polymerase chain reaction (PCR). Screening of a porcine peripheral T cell cDNA library with these PCR fragments led to the isolation of porcine TcR alpha, beta, gamma and delta chain clones. Sequence analysis of these clones and the respective PCR fragments demonstrated the existence of one alpha, one beta, three gamma and one delta chain isotype. Comparisons of the deduced amino acid sequences of the constant region with other species revealed a significant homology. For two of the three identified porcine gamma chain insertions of 38 and 40 amino acids were found within the hinge region. In addition, our sequence data demonstrate a high variability in the cytoplasmic C gamma domain among the three porcine TcR gamma isotypes as well as between species, which might be of structural and/or functional significance. Comparison with biochemical data indicate the existence of four porcine TcR gamma isotypes.

A comparative review of human and equine leucocyte differentiation antigens

Monoclonal antibody technology has allowed the recognition and study of numerous leucocyte antigens in man and laboratory animals for over a decade. Numerous advances in the understanding of immune responses and immunopathology have resulted. In recent years equine researchers have started to develop similar reagents, which now offer a powerful tool to investigators of equine immunology and disease.