Prominence of gamma delta T cells in the ruminant immune system

The lymphoid systems of sheep and cattle contain a large number of gamma delta T cells, in striking contrast to the lymphoid systems of humans and mice. In neonatal animals particularly, these cells comprise the predominant fraction of T cells in the blood. Here Wayne Hein and Charles Mackay discuss what is currently known about the ontogeny, phenotype, tissue distribution and function of gamma delta T cells in ruminants. There are a number of interesting molecular features that characterize ruminant gamma delta T cells, but these do not entirely explain the high frequency of use of the gamma delta T-cell receptor in these animals. Studies on sheep, cattle or other animals that preferentially use gamma delta T cells should provide insights into the biological significance of the existence of two distinct forms of the T-cell receptor.

Effect of molecular weight on the lymphatic absorption of water-soluble compounds following subcutaneous administration

The lymphatic absorption of four water-soluble compounds with different molecular weights (MW) was determined by measuring their cumulative recovery in lymph draining from the site of s.c. administration in sheep. The cumulative recoveries (% of dose, mean +/- SD; N = 3) were 4.0 +/- 1.5 (5-fluoro-2'-deoxyuridine, MW 246.2), 21.0 +/- 7.1 (inulin, MW 5200), 38.6 +/- 6.7 (cytochrome c, MW 12,300), and 59.5 +/- 7.7 [human recombinant interferon (rIFN) alpha-2a, MW 19,000], respectively. Our data show that in the investigated MW range, there is a linear relationship between the molecular weight and the proportion of the dose absorbed lymphatically. An increase in molecular weight results in an increased lymphatic absorption. Molecules with MW greater than 16,000 are absorbed mainly by the lymphatics which drain the application site. The knowledge gained in this investigation may help to improve the mode of administration and therapeutic efficacy of endogenous proteins whose targets are lymphoid cells (e.g., interferons, interleukins). Practical implications for the clinical use of such proteins are discussed.

Hypermutation generating the sheep immunoglobulin repertoire is an antigen-independent process

Somatic hypermutation of light chain V genes during development of B cells in sheep ileal Peyer's patches was studied in three experimental conditions: in sterile fragments of the ileum surgically isolated from the gut during fetal life, in germ-free sheep, and in animals thymectomized during early fetal life. The somatic mutation pattern was found identical to control tissues in all three experiments. The same age-dependent amount of mutations, a higher than theoretical R/S ratio in complementarity-determining regions (CDRs), and a similar clustering of mutations in CDRs were observed. The mechanism, as estimated from the silent mutation pattern, appears to target mutations to CDRs; moreover, the major V lambda genes have a specific codon usage with a high purine content at the first two bases of the codons and a low content at the third position, which, together with a specific targeting of mutations to purines, favors replacement mutations in CDRs.

Tissue-specific migration pathways by phenotypically distinct subpopulations of memory T cells

A proportion of T cells recirculate in a tissue-selective manner. Recent studies which showed that the skin-tropic subset of T cells was of memory/activated type, led us to examine whether the preferential homing of T cells to the gut also involved memory T cells, and if so whether these memory T cells were phenotypically distinct from other memory T cells. Lymphocytes migrating through the gut and the skin of sheep was collected by cannulating the lymphatic ducts draining these tissues. Both naive and memory T cells were found to recirculate through the gut, although only memory T cells migrated through the skin. However, when T cells from the gut were labeled with fluorescein isothiocyanate and assessed for their migration back to the gut, it was the memory population which showed a tropism for the gut. Gut-tropic memory T cells migrated poorly through the skin, indicating that these cells were distinct from skin-tropic memory T cells. This was confirmed by phenotypic analysis. Gut memory T cells expressed very low levels of the alpha 6 and beta 1 integrins, in contrast to skin memory T cells which expressed high levels. There was no evidence for heterogeneity within the naive T cell population, which migrated preferentially to lymph nodes. This migration pattern could be explained in part by the high expression of the L-selectin (lymph node homing receptor, LAM-1) on naive T cells, in contrast to memory T cells from gut or skin which were mostly L-selectin negative. These results in sheep indicate that subsets of alpha/beta memory T cells show tissue-selective migration patterns, which probably develop in a particular environment following encounter with antigen.

A large proportion of bovine T cells express the gamma delta T cell receptor and show a distinct tissue distribution and surface phenotype

The numbers, phenotype, and tissue distribution of gamma delta T cells in cattle were studied using two monoclonal antibodies (mAbs) which react with the bovine gamma delta T cell receptor (TCR). Both mAbs stained 20-40% of T cells in peripheral blood, and immunoprecipitated molecules of 44 and 36 kd (reduced) and 70-80 kd (non-reduced). In cattle the majority of circulating gamma delta T cells showed a distinct surface phenotype; they expressed T19, a 215 kd molecule described in sheep and cattle which marks only gamma delta T cells. Bovine gamma delta T cells were also CD2-, CD4-, and mostly CD8-, and failed to express CD6, a molecule possibly involved in T cell activation. The distribution of gamma delta T cells in cattle lymphoid tissues differed markedly from that in humans, in that bovine gamma delta T cells were concentrated around lymph node trabeculae and were usually sparse or absent from the B cell and T cell domains of lymph nodes. Like most other species studied, gamma delta T cells in cattle were localized to epithelial surfaces, particularly within the skin and intestine, indicating that it was at these sites where gamma delta T cells functioned. Our results provide further evidence for the unusual localization, recirculation pattern, and phenotype of gamma delta T cells, and also show that some features of gamma delta T cells can differ quite markedly from species to species.

Unusual expression of CD2 in sheep: implications for T cell interactions

The CD2 adhesion/activation molecule on the surface of mammalian T lymphocytes binds to a ubiquitous receptor, LFA-3. We show that CD2 in sheep differs significantly in its expression from CD2 in humans, and this most likely relates to the high level of expression of the sheep LFA-3 molecule. In sheep, in contrast to man, CD2 was weakly expressed on peripheral T cells and thymocytes. Moreover, a large subset of T cells identified by the monoclonal antibody T19 and considered to be gamma/delta receptor-bearing T cells completely lacked the CD2 molecule. T19+ cells constituted up to 50% of peripheral blood T cells in lambs, and 20-30% of T cells in older sheep, whereas the CD4+ and CD8+ subsets, which are both CD2+, constituted relatively small subsets in peripheral blood. Only those T cells which did express CD2 adhered as "rosettes" to dendritic cells, and the localization of CD2 to the membrane junction indicated that CD2 was critical for this adhesion. However, CD2 adhesion was not necessary for CTL-mediated killing of allogeneic target cells, since T19+ cells generated in bulk mixed lymphocyte culture were extremely efficient at killing appropriate target cells. Some of the behavioral differences between T19+ and CD4+/CD8+ subsets might be explained by the presence or absence of CD2. The results also indicate that the expression of CD2 (and LFA-3) may differ markedly between species.

TCR gamma delta+ cells are prominent in normal bovine skin and express a diverse repertoire of antigen receptors

More than 80% of T cells in bovine skin localized in the superficial 0.5 mm of the dermis. Only 3% occurred within the epidermis or made contact with the stratum basale while the remainder occupied deeper dermal sites. The gamma delta-T-cell receptor (TCR) was expressed by 44% of T cells in skin and 39% and 35% expressed, respectively, the CD4 and CD8 markers. Some cells co-expressed CD8 and the gamma delta TCR. A highly diverse repertoire of gamma delta TCR was expressed in skin due mainly to the usage of multiple V delta segments and to extensive sequence variation at the junctions of both TCR gamma and TCR delta chains. However, a single receptor isotype was used. Transcripts encoding several new components of the bovine gamma delta TCR were identified, including three new V gamma segments, the C gamma 5 region and 13 new functional V delta segments. Taken together with earlier findings, these results emphasize that ruminant gamma delta T cells express exceptionally diverse antigen receptors and suggest they may have a more elaborate recognitive capacity than do their counterparts in other species.

Divergent evolution of T cell repertoires: extensive diversity and developmentally regulated expression of the sheep gamma delta T cell receptor

Sheep gamma delta T cells express an unprecedented repertoire of antigen receptors contributed by increased diversity in both variable and constant region gene segments. Variable region diversity results mainly from the utilization of a large family of duplicated V delta genes that have retained two distinct hypervariable segments comparable with the complementarity determining regions present in other antigen receptor V genes. This implies that sheep V delta chains have been intensely selected during evolution, probably at sites involved in ligand recognition. The sheep gamma delta heterodimer occurs in at least five isotypic variants formed by the association of a single C delta segment with one of five functional C gamma segments, each with distinctive hinge regions. Our analysis also shows that the establishment of a normal peripheral repertoire is both developmentally regulated and dependent on the continual presence of a functional thymus during ontogeny. The existence of an expanded V gene repertoire and multiple receptor isotypes together with the prominence of gamma delta T cells in the sheep immune system argues that this lineage of T cells has a more elaborate functional role in this evolutionary pathway.

A single predominantly expressed polymorphic immunoglobulin VH gene family, related to mammalian group, I, clan, II, is identified in cattle

In order to understand the generation of antibody diversity in cattle, seven cDNAs, from heterohybridomas secreting bovine IgM and IgG1 antibodies, were cloned and structurally analyzed for rearranged bovine VDJ genes. All of the seven bovine VH genes, together with four available bovine VH gene sequences, shared a high nucleotide sequence homology (84.2-93.5%). Based upon the criteria of nucleic acid homology > or =80%, all of the bovine VH gene sequences isolated from the expressed antibody repertoire constitute a single VH gene family, which we have designated as bovine VH1 (Bov VH1). An analysis of 44 bovine IgM-secreting mouse x cattle heterohybridomas, originating from polyclonally-activated PBLs from bovine leukemia virus-infected cattle, revealed that all of these expressed Bov VH1 (100%) based upon DNA sequencing and Northern dot blot. The bovine VH genes showed highest DNA sequence similarity, ranging between 81.5 and 87.6%, with a single sheep VH gene family (related to human VH4) and are, thus, closest to the VH genes from another ruminant species. The Bov VH1 gene family is most homologous to the murine VH Q-52 (71.8-78%) and human VH4 (67.4-69.8%) gene families, which belong to mammalian group, I, clan, II, VH genes. The CDR3 length of rearranged bovine VDJ genes is characteristically long (15-23 amino acids). The bovine JH gene segments were most homologous to human JH4 (82.1-87.2%) and JH5 (84.6-89.7%) genes, suggesting the existence of at least two JH gene segments. An analysis of CDRs provides evidence that somatic hypermutations contribute significantly to the generation of antibody diversity in cattle. Southern blot analysis of BamH I, EcoR I and Hind III digested genomic DNA from four cattle breeds (Holstein, Jersey, Hereford and Charolais) revealed three RFLP patterns; the genomic complexity of Bov VH1 ranged between 13 and 15 genes. These observations provide evidence for polymorphism at the bovine Ig-VH locus, similar to that seen in mice and humans.

Immune rejection of Trichostrongylus colubriformis in sheep; a possible role for intestinal mucus antibody against an L3-specific surface antigen

Sheep that have been immunized by multiple truncated infections with the parasitic nematode Trichostrongylus colubriformis contain anti-larval activity in their intestinal mucus and high-speed mucus supernatants. This activity induces T. colubriformis L3 to clump in vitro and causes a significant reduction in larval establishment in naive sheep after infusion of larvae and mucus into the intestinal lumen via a duodenal cannula. In this report, we provide evidence that one factor contributing to the anti-larval activity of immune mucus is antibody against a 35-kDa L3-specific cuticular antigen. The anti-larval activity in mucus is > 100 kDa by membrane filtration, is heat labile and sensitive to either protease digestion or reduction with DTT. Immunoblotting showed that mucus and supernatants of ultracentrifuged mucus from immune sheep contained IgG1 and IgA antibodies that recognized predominantly a larval antigen with an estimated molecular weight of 35 kDa on SDS-PAGE. Antibodies eluted from the surface of washed larvae that had been incubated in immune mucus also reacted specifically with the 35 kDa antigen on blots of larval homogenate. Immunofluorescence and immunogold electron microscopy showed that the 35 kDa antigen is present on the epicuticle of L3 and is shed during the moult to L4. The antigen is not present in eggs, L1, L2, L4 or adult worms and is found only in extracts of sheaths and L3 before infection and up to 4 days after infection. We hypothesize that the binding of antibody to the larval surface prevents larvae from establishing at their preferred site, causing them to be eliminated from the intestine. Monoclonal antibody PAB-1 recognizes the 35 kDa T. colubriformis larval antigen and also cross-reacts with antigens of similar molecular weight on blots of L3 extracts of the parasitic nematodes Haemonchus contortus and Ostertagia circumcincta; and with a 22-kDa antigen on blots of L3 extracts from Cooperia curticei and Nematodirus spathiger. This indicates that an antigenically related surface antigen with immunizing potential is present on several nematode species and can be identified by mAb PAB-1. The 35 kDa T. colubriformis larval antigen and related molecules in other nematodes are potential novel targets for stimulating host-protective immunity against nematode infections.

Differential peripheral expansion and in vivo antigen reactivity of alpha/beta and gamma/delta T cells emigrating from the early fetal lamb thymus

The concentrations of different lymphocyte subsets in the blood of lambs which had been thymectomized (Tx) in utero between days 67-75 of fetal gestation were measured at birth and at various intervals during the first year of life. Compared to thymus-intact (Ti) controls, Tx lambs were severely depleted of both alpha/beta and gamma/delta T cells at birth (less than 10% of control levels). The majority of the residual alpha/beta T cells present in Tx lambs at birth were CD4+CD8-. As the Tx lambs aged, the concentration of alpha/beta T cells in blood increased steadily to reach levels around 50% of control values. In contrast, the circulating gamma/delta T cells did not expand in Tx animals and remained barely detectable throughout the observation period, although these cells accounted for 30%-60% of the T cells in the blood of Ti lambs. The expansion of alpha/beta but not gamma/delta T cells was also reflected in changes in the cellular composition of solid lymphoid organs in Tx lambs. B cell numbers were similar in both groups at birth but Tx lambs were persistently B lymphopenic from 3 weeks of age onwards. The alpha/beta T cells that had expanded in Tx lambs responded to stimulation with bacterial antigens in a way that was qualitatively similar to the response in Ti lambs. By contrast, the few gamma/delta T cells in Tx lambs responded abnormally. Our results show that although sheep alpha/beta and gamma/delta T cells are equally thymus dependent during ontogeny, the early fetal thymic emigrants which establish the two T cell lineages in the periphery have strikingly different antigen reactivities and capacities for self-renewal and expansion.

Vaccines against veterinary helminths

The majority of attempts to develop commercial vaccines for veterinary helminths have focussed on identifying protein antigens, which could be formulated as protective vaccines. Notable successes have been achieved for some cestode parasites, where recombinant proteins have been developed into highly effective vaccines. Although effective protection can also be obtained using some nematode proteins in their native forms, it has not yet been possible to formulate commercially successful vaccines for other helminth parasites of veterinary significance. Increasing evidence suggests that parasite glycan moieties may provide an alternative source of vaccine antigens, and increased attention is now being given to this class of compounds. In addition to identifying candidate protective antigen(s), an increased research effort is needed to develop appropriate strategies for the formulation and delivery of helminth vaccines.

Total and nematode-specific IgE responses in intestinal lymph of genetically resistant and susceptible sheep during infection with Trichostrongylus colubriformis

Total and antigen-specific IgE responses in afferent (AIL) and efferent (EIL) intestinal lymph of sheep with a nematode resistant (R) or susceptible (S) genotype during challenge infection with the intestinal nematode parasite Trichostrongylus colubriformis were examined. Within each sheep line, lambs with a nematode naive or nematode field-primed pre-challenge status were used. Total IgE level in AIL and EIL was dependent on nematode infection and was further influenced by genotype or the immune phenotype (nematode immune mean FEC+/-SDM=77+/-179 or non-immune mean FEC+/-SDM=4016+/-4318) of the animal. During T. colubriformis challenge immune animals had higher levels of total IgE in lymph than non-immune sheep, R line sheep had higher concentrations of total IgE than S line sheep, and field-primed animals had higher total IgE levels than nematode naive animals. Concentrations of total IgE were consistently higher in AIL than EIL or serum and were higher in lymph draining the proximal than the distal jejunum demonstrating that polyclonal IgE in AIL was largely derived from the intestinal mucosa of the anatomical compartment where the nematodes reside. The consistently higher concentration of total IgE in AIL was dependent on phenotype or genotype and in S genotype sheep also on the pre-challenge status. Concentrations of nematode specific IgE were significantly higher in EIL than AIL indicating a preference for the production of IgE reacting with excretory secretory products of the infective T. colubriformis larvae in the regional lymph node.

Ontogeny, morphology and tissue distribution of a unique subset of CD4-CD8- sheep T lymphocytes

The morphology, distribution and ontogeny of the 197+ T lymphocyte subpopulation is described. Cells were identified by immunofluorescent and immunoenzymic staining of cell suspensions and tissue sections. In the circulation, 197+ cells are small and regular, indistinguishable in size from peripheral CD4+ and CD8+ cells, with little cytoplasm and a large amount of condensed chromatin. In the post-natal animal they are unevenly distributed, being most common in the circulatory pathways, particularly in the blood. In the thymus they chiefly localize in the regions around Hassal's corpuscles and medullary blood vessels. They are totally absent from B cell areas in all tissues. They are the last of the T cells to appear in ontogeny, and are first detected in the thymus. Their frequency in blood is age-dependent with peak levels occurring perinatally. There is a post-natal decline in the frequency of 197+ cells in ileocaecal but not in prescapular lymph nodes. We conclude that these T cells differ from the more commonly described T cells, not only in their surface expression of the CD4, CD8 and T19 antigens, but also in the time of their first appearance, their age-related prevalence and their distribution between and within tissues.

An abattoir survey of tuberculosis in feral buffaloes

Tuberculosis lesions were found in 193 (1.7%) of 11,322 buffaloes examined during routine post-mortem inspection at 2 export abattoirs. The prevalence of tuberculosis in buffaloes supplied from 17 separate farms ranged from 0.3% to 8.22%, with the highest levels occurring on the coastal plains. Lesions were confirmed to one major body region in 50 of 72 randomly chosen cases of tuberculosis and to 2 or more regions in 22 cases. Thoracic lesions occurred in 65 of the 72 cases, abdominal lesions in 19, head lesions in 18 and carcase lesions in 9. In the thoracic cavity, lesions occurred most frequently in mediastinal and bronchial lymph nodes. In the head region the retropharyngeal lymph node was most frequently involved, in the abdominal cavity, the liver, and in the carcase, the deep inguinal lymph node. Tuberculosis lesions in buffaloes had a lardaceous consistency and were paler in colour and less calcified than those normally exhibited by cattle. Mycobacteria were isolated from 30 to 31 lesion samples submitted for bacteriological examination. Of the isolates, 25 were identified as Mycobacterium bovis, 3 as M. avium-intracellulare-scrofulaceum complex, one as M. fortuitum and one as M. flavescens. The M. bovis isolates from buffaloes showed minor cultural differences to those normally characteristic of bovine isolates.

Mixed micelles as a proliposomal, lymphotropic drug carrier

Four lipophilic, low molecular weight drugs solubilized in phosphatidylcholine-bile salt mixed micelles were injected s.c. into the hind legs of sheep and their cumulative recoveries in lymph draining from the site of application were determined. Surprisingly, the cumulative recoveries (percentage of dose) varied between less than 1 and 60%. We found that there is a correlation between the lipophilicity of the drug (log P octanol/water approximately Rm degrees value) and the proportion of the dose absorbed by the lymphatic route. Drugs with Rm degrees values greater than 10 are absorbed preferentially by the lymphatics (greater than 50% of dose), whereas compounds with Rm degrees values less than 4 are hardly absorbed at all by the lymphatics (less than 10% of dose). By applying the prodrug principle we demonstrated that it is also possible to target drugs with Rm degrees values less than 4 to the lymphatics. Furthermore, the analysis of the collected lymph samples by gel filtration, quasi-elastic light scattering, and electron microscopy revealed that, following s.c. administration, mixed micelles are converted into homogeneous, unilamellar vesicles. In conclusion, these results suggest that mixed micelles may represent a suitable delivery system for low molecular weight drugs whose targets are lymphoid cells. In addition, for drugs where liposomal application leads to a therapeutic advantage, the thermodynamically stable mixed micelle could be a good alternative to the liposome. However, for both applications a high drug lipophilicity is a prerequisite.

Molecular cloning of sheep T cell receptor gamma and delta chain constant regions: unusual primary structure of gamma chain hinge segments

The primary structure of sheep T cell receptor (TcR) gamma and delta chain constant (C) regions has been determined by cDNA cloning. A comparison of the nucleotide and deduced amino acid sequences of the sheep chains with known human and mouse sequences shows that the primary structure of the immunoglobulin, transmembrane and cytoplasmic C gamma domains and all of the C delta region has been substantially conserved. However, the hinge or connector region of sheep gamma chains differs significantly from all known TcR chains. Clones representing two different sheep C gamma genes were isolated and both contain additional sequence in this region, making them the longest TcR chains so far identified. The hinge region of both sheep C gamma sequences contains two additional cysteine residues and a motif of five amino acids (TTESP or TTEPP) which has been triplicated in one of the clones. Other repetitive segments of 13-17 amino acids could also be identified suggesting that, as in the human C gamma 2 gene, this region of the sheep genes could have arisen from an exon duplication or triplication event. Southern blot analysis of sheep DNA confirmed the presence of one C delta gene and at least two C gamma genes. A restriction fragment length polymorphism that is probably associated with allelic sequence variation in the sheep C delta gene was detected in DNA from different animals. Although the essential structure of the gamma/delta TcR appears well conserved through evolution, the marked heterogeneity evident in the hinge region of gamma chains both within and between species, and particularly the presence of additional cysteine residues in the sheep sequences, may be of structural and functional importance.

T cell receptor gene expression in sheep: differential usage of TcR1 in the periphery and thymus

We have isolated cDNA clones for each chain of the sheep T cell receptor (TcR) and used these to analyze TcR gene expression in thymocyte and peripheral T cell subsets. Outer cortical thymocytes expressed a low level of mature message for all TcR chains suggesting that intrathymic precursors for the alpha/beta and gamma/delta lineages occur in this population. Inner cortical and medullary thymocytes expressed high levels of mature alpha/beta transcripts, low levels of mature delta transcripts but no detectable gamma message. Mature alpha/beta transcripts were detected in peripheral CD4+ lymphocytes and these as well as CD8+ cells expressed a surface heterodimer of 85 kDa which resolved into 40- and 50-kDa subunits after reduction. Peripheral CD4-CD8-lymphocytes, which in sheep are marked by the T19 antigen and may account for up to 60% of T cells in blood, expressed a surface heterodimer of 75 kDa. The T19+ cells had high levels of mature delta and truncated beta transcripts in their cytoplasm but did not express the C gamma gene detected in DN thymocytes, although they seem to share V gamma and/or J gamma elements. Both forms of the sheep TcR are associated with CD3 molecules on the cell surface. These results show that (a) in contrast to the situation in rodents and humans, a large proportion of peripheral sheep lymphocytes use TcR gamma/delta; (b) the proportion of T cells in the periphery which use TcR gamma/delta is greater than in thymus; and (c) CD4-CD8- cells in thymus and periphery (T19+) use the same C delta gene but appear to use different C gamma genes, suggesting that in sheep there may be more than one lineage of lymphocytes expressing TcR gamma/delta.

Characterization of a 35-kDa carbohydrate larval antigen (CarLA) from Trichostrongylus colubriformis; a potential target for host immunity

In an accompanying paper we show that antibodies in intestinal mucus that recognize a 35-kDa antigen from the surface of the L3 stage of the sheep intestinal nematode parasite, Trichostrongylus colubriformis, are strongly associated with immune rejection of L3 in a truncated infection model of immunity in sheep. Monoclonal antibody PAB-1 was used to immunopurify this antigen from T. colubriformis L3. The antigen is resistant to digestion with a range of proteases including proteinase K and does not stain on gels or blots treated with protein-detecting reagents but does stain with carbohydrate-detecting reagents. The antigen is also resistant to degradation by the action of lipases and is not soluble in organic solvents, suggesting that lipid components are not present or not accessible. Treatment with glycosidases does not affect the antigen, indicating either that sialic acid and N-linked or O-linked sugars are not present or that they are not accessible to enzyme attack. The antigen is not destroyed by harsh alkaline degradation with up to 8 m NaOH with or without borohydride reducing agent, or by extensive hydrazinolysis. Strong acid hydrolysis with trifluoroacetic acid or boiling in hydrochloric acid for 20 min does destroy the antigen. The antigen migrates as a poorly defined high molecular weight complex on native electrophoresis gels, but is detected as a major band at 35 kDa on SDS PAGE either by carbohydrate staining or by immunoblotting with antibody from immune sheep intestinal mucus and with mAb PAB-1. Proteinase K digestion and alkaline degradation of extracts from L3 of 10 other parasitic nematode species revealed that L3 of each species contained a carbohydrate staining molecule which can be detected by mAb PAB-1 and by mucus antibody from immune sheep. Because antibodies in intestinal mucus are directed against these antigens and may be responsible for protective immunity, carbohydrate larval antigens (CarLA) could represent a new family of molecules with potential as targets for stimulating host immunity.

An abattoir survey of diseases of feral goats

Caseous lymphadenitis was the most frequently encountered pathological condition in 3,720 feral goats examined during routine meat inspection procedures. Among 9 separate consignments of animals, the prevalence of infection averaged 7.4% (range 0.3% to 18.8%). The majority of lesions were seen in lymph nodes draining superficial body areas although many also occurred in internal nodes and organs. Corynebacterium ovis was isolated from 25 of 32 lesions submitted for bacteriological examination. Other conditions regularly encountered included pneumonia, cysticercosis, sarcosporidiosis and lice infestation, while myonecrosis, pleurisy, pericarditis, nephritis, hepatitis, cirrhosis and mite infestation were only occasionally found. A total of 171 serum samples were collected and tested against 17 antigens. Samples from 57.9% and 51.5% of goats showed positive serological reactions to the antigens for sarcosporidiosis and Q fever respectively.

Structural and functional evolution of the extracellular regions of T cell receptors

The primary structure of T cell receptor (TcR) heterodimers has been elucidated to varying degrees in 11 vertebrate species and the availability of these sequences provides a broader perspective for reassessing TcR evolution. Many features of the alpha beta TcR have been well conserved between divergent taxa whereas the structure and diversity of the gamma delta TcR is more variable. An alternative evolutionary scheme is presented whereby the gamma delta TcR and Ig molecules represent the earliest separation between specific cell mediated and humoral immunity with the alpha beta TcR emerging later. It is proposed that a set of ligands expressed on epithelia mediated the earliest selection of gamma delta T cells and B cells and was used as an antigen presentation substrate by gamma delta T cells. A subset of the earliest selection ligands became expert at binding small peptide fragments and the emergent 'classical' MHC molecules then co-evolved with the alpha beta TcR as obligate ligand-receptor pairs. Progression between the major stages in this sequence followed from adaptations in the selecting and presenting ligands and can be characterized as MHC 'capture'.

Cellular composition of peripheral lymph and skin of sheep defined by monoclonal antibodies

The surface phenotype of cells in peripheral lymph collected from afferent lymphatics leading to the popliteal lymph node of sheep was determined using a panel of monoclonal antibodies (mAbs). The majority of lymphocytes (83.5%) expressed the sheep pan-T cell antigen and only 13.3% bore surface immunoglobulin molecules. All peripheral T cell subsets occurring in sheep were detected; 50.2% of lymphocytes were positive for mAb SBU-T4 (T helper), 7.3% were positive for mAb ST-8 (T cytotoxic), and 8.4 and 43.0% expressed T subset markers recognized by mAbs 197 and T-80, respectively. Major histocompatibility complex (MHC) class I antigens were detected on 71.1% of lymphocytes and MHC class II antigens on 21.8%. The macrophage/veiled cells found in peripheral lymph did not express lymphocyte subset markers but were positive for MHC class I and II antigens, the sheep homologue of T6 antigen, leukocyte common antigen and mAb 175 (myeloid/erythroid). Macrophage-like cells occurring in the epidermis of skin taken from the lower hindleg gave positive staining reactions to the same mAbs which stained the macrophage/veiled cells in peripheral lymph. These results illustrate differences between the migration of lymphocyte subsets through nonlymphoid as compared to lymphoid tissues and point to a possible developmental or migratory relationship between the macrophage-like cells in skin and those in afferent popliteal lymph.

Lymph node homing cells biologically enriched for gamma delta T cells express multiple genes from the T19 repertoire

Sheep gamma delta T cells have been shown serologically to express T19, a membrane protein of 180-200 kDa which is a member of the scavenger receptor superfamily. Previous work from this laboratory resulted in the detection of a multigene family of T19-like genes in the sheep genome. In this study nucleotide sequences from several T19 genes were determined and are reported along with the corresponding segments of a number of expressed mRNA molecules. A segment of a single sheep T19-like gene was sequenced and these data, along with the corresponding sequences from cloned T19-like cDNA molecules from sheep and cow, were used to design an oligonucleotide primer system suitable for amplification of corresponding segments of many T19 genes and their cDNAs. Between 30 and 40% of cloned T19 genes were amenable to amplification using the selected primers, and sequence analysis of cloned PCR products confirmed that different T19 genes encode unique amino acid sequences. The expression of multiple T19 genes was established using cDNA molecules obtained from a single sample of sheep lymphocyte mRNA. The possible role of the T19 family of genes is discussed.

Functional characteristics of 197+ CD4- CD8- sheep T lymphocytes: expansion and differentiation of peripheral T cells

This report describes the results of functional studies on the CD3+ 197+ CD4- CD8- TCR gamma/delta + peripheral T lymphocyte of sheep. Cell types were identified by immunofluorescent and immunoenzymic staining and separated by fluorescence activated flow cytometry. Newly synthesized DNA was labelled in vivo by incorporation of 5-bromo-2-deoxyuridine (BrdU), and total DNA by in vitro incubation with propidium iodide. Cells were challenged in vivo with alloantigens, in vitro with alloantigens or a range of mitogens, and activation/differentiation was assessed by determination of cell number, phenotype, and thymidine incorporation. In normal lambs the 197+ cells showed no in vivo DNA synthesis except at a low level in the ileocaecal lymph node. A similarly low level of synthesis in the prescapular node was induced by local allogeneic challenge. A higher proportion of 197+ cells than of other T cells isolated from blood and lymph had G2/M phase DNA content, while very few had S phase DNA content. The response of 197+ cells in terms of change in relative numbers following in vivo allogeneic challenge was quite different to that of CD4+ or CD8+ cells. Instead of rising to a peak at 5-8 days after challenge and then declining, the percentage of 197+ cells rose steadily with no evidence of decline by 14 days. Purified 197+ cells were activated in vitro by phytohaemagglutinin (PHA) and concanavalin-A (Con-A) but not by B cell mitogens; such activation was dependent on the inclusion of feeder cells or interleukin-2 (IL-2).(ABSTRACT TRUNCATED AT 250 WORDS)