Induction of gamma/delta T cells in murine salmonellosis by an avirulent but not by a virulent strain of Salmonella choleraesuis

Salmonellosis: host immune responses and bacterial virulence determinants

The lifestyle of bacterial pathogens requires them to establish infection in the face of host immunity. Upon entering a potential host, a variety of interactions are initiated, the outcome of which depends upon a myriad of attributes of each of the participants. In this review we discuss the interactions that occur between pathogenic Salmonella species and the host immune systems, but when appropriate to broaden perspective, we have provided a general overview of the interactions between bacterial pathogens and animal hosts. Pathogenic Salmonella species possess an array of invasion genes that produce proteins secreted by a specialized type III secretion apparatus. These proteins are used by the bacteria to penetrate the intestinal mucosa by invading and destroying specialized epithelial M cells of the Peyer's patches. This maneuver deposits the bacteria directly within the confines of the reticuloendothelial system. The host responds to these actions with nonspecific phagocytic cells and an inflammatory response as well as by activating specific cellular and humoral immune responses. Salmonella responds to this show of force directly. It appears that the bacteria invade and establish a niche within the very cells that have been sent to destroy them. Efforts are underway to characterize the factors that allow these intracellular bacteria to customize intracellular vacuoles for their own purposes. It is the constant play between these interactions that determines the outcome of the host infection, and clearly they will also shape the evolution of new survival strategies for both the bacterium and the host.

gamma/delta and other unconventional T lymphocytes: what do they see and what do they do?

T lymphocytes recognize specific ligands by clonally distributed T-cell receptors (TCR). In humans and most animals, the vast majority of T cells express a TCR composed of an alpha chain and a beta chain, whereas a minor T-cell population is characterized by the TCR gamma/delta. Almost all of our knowledge about T cells stems from alpha/beta T cells and only now are we beginning to understand gamma/delta T cells. In contrast to conventional alpha/beta T cells, which are specific for antigenic peptides presented by gene products of the major histocompatibility complex, gamma/delta T cells directly recognize proteins and even nonproteinacious phospholigands. These findings reveal that gamma/delta T cells and alpha/beta T cells recognize antigen in a fundamentally different way and hence mitigate the dogma of exclusive peptide-major histocompatibility complex recognition by T cells. A role for gamma/delta T cells in antimicrobial immunity has been firmly established. Although some gamma/delta T cells perform effector functions, regulation of the professional and the nonprofessional immune system seems to be of at least equal importance. The prominent residence of gamma/delta T cells in epithelial tissues and the rapid mobilization of gamma/delta T cells in response to infection are consistent with such regulatory activities under physiological and pathologic conditions. Thus, although gamma/delta T cells are a minor fraction of all T cells, they are not just uninfluential kin of alpha/beta T cells but have their unique raison d'être.

The Salmonella dublin virulence plasmid does not modulate early T-cell responses in mice

The virulence plasmid in Salmonella dublin mediates systemic infection in mice and cattle. The role of gamma delta T cells or hepatic extrathymic T cells has recently been reported to be important in the control of the early stage of Salmonella choleraesuis infections of mice. Here, we report on T-cell responses in conventional mice after challenge with a virulent strain of S. dublin carrying a virulence plasmid or with a strain cured of the plasmid. Over a period of 4 days postinfection, when both strains could be compared, similar changes in alpha beta and gamma delta T-cell subsets in peritoneal cavities, livers, and spleens were recorded, demonstrating no clear role of the virulence plasmid in modulation of early T-cell responses. To investigate further the role of the virulence plasmid in pathogenesis, the growth of the plasmid-cured strain was assessed in SCID, SCID bg, and irradiated mice. During the first 6 days after infection, there was no statistically difference in the net growth of Salmonella cells in the livers and spleens of SCID and SCID bg mice compared with conventional BALB/mice. This observation excludes a key role for a T- or B-cell-mediated immune response in controlling the initial growth of the plasmid-cured S. dublin strain. Thereafter, the immunocompromised mice were no longer able to control infection, although SCID mice were more efficient at controlling net bacterial multiplication than SCID bg mice, potentially implicating NK cells in the control of infection in SCID mice. The early control of net bacterial multiplication in the spleens and livers of BALB/c mice was ablated by whole-body X-irradiation. Both wild-type and plasmid-cured strains multiplied significantly more rapidly in irradiated than in conventional BALB/c mice. However, the numbers of wild-type bacterial still increased more rapidly than in the numbers of the cured strains. These results are consistent with a role of the S. dublin virulence plasmid in promoting in vivo growth of Salmonella cells.

Evidence for the early recruitment of T-cell receptor gamma delta+ T cells during rat listeriosis

We have previously reported that heat-shock protein (hsp) 60-reactive T-cell receptor (TCR)gamma delta+ T cells appear in the peritoneal cavity during the early stage of infection with Listeria monocytogenes in mice. In this study, we examined the kinetics of TCR gamma delta+ T cells during listeriosis in F344 rats by flow cytometry using a V65 monoclonal antibody (mAb) directed to a constant determinant of rat TCR gamma delta chains. TCR gamma delta+ T cells significantly increased in the peritoneal cavity on day 6 and then decreased by day 10 after infection, in parallel with the kinetics of hsp60 expression in the peritoneal macrophages during listeriosis in F344 rats. Most of the early appearing TCR gamma delta+ T cells were of the CD4- CD8 alpha beta+ CD5+ lymphocyte function-associated antigen (LFA)-1 alpha high CD45RC- interleukin-2 receptor (IL-2R) alpha- phenotype, although a significant fraction of the TCR gamma delta+ T cells expressed CD8 alpha only. The increase in TCR gamma delta+ T cells during listeriosis was prominent in F1 (F344 x Lewis) rats but only marginal in Lewis rats, which was correlated with the expression level of hsp 60 in the peritoneal macrophages. The peritoneal TCR gamma delta+ T cells in naive F344 rats appeared to proliferate significantly in response to recombinant hsp 60 (rhsp 60) derived from Mycobacterium bovis bacillus Calmette-Guérin (BCG). These results imply that the early appearance of hsp 60-reactive TCR gamma delta+ T cells during listerial infection can be generalized across species.

Ontogenic development and tissue distribution of V gamma 1-expressing gamma/delta T lymphocytes in normal mice

A hamster monoclonal antibody (mAb) recognizing an epitope in the V gamma 1-J gamma 4-C gamma 4 chain of the gamma/delta T cell receptor has been generated. Using this mAb, we have quantitated the occurrence of V gamma 1-bearing gamma/delta T cells in the developing thymus and in the lymphoid organs and several epithelia of adult mice. The V gamma 1-expressing cells constitute a minor gamma/delta T cell subpopulation during fetal and early postnatal life, but they constitute a major population of gamma/delta T cells in the thymus and in the peripheral lymphoid organs in adult mice. In addition, we found that V gamma 1-bearing cells comprise a large proportion (15-60%) of the gamma/delta T cells present in the intestinal epithelium (i-IEL) in all strains of mice tested. V gamma 1+ i-IEL are present in athymic (nude) mice and in antigen-free mice, demonstrating that they can develop extrathymically and that their presence in the intestinal epithelium is independent of the antigenic load of the gut. Our results show that V gamma 1-bearing lymphocytes account for the largest population of gamma/delta T cells in the mouse. This population includes a thymus-dependent component that homes to the secondary lymphoid organs and a thymus-independent component that constitutes a major fraction of the gamma/delta i-IELs.

Conversion of Salmonella typhimurium to L-forms contributes to the maintenance of acquired immunity against murine typhoid

Conversion of Salmonella typhimurium to L-forms, both in vitro and in vivo, resulted in the expression of proteins cross-reacting to the mycobacterial 65,000 MW heat-shock protein (hsp). Immunization of C3H/HeJ mice with a protective dose of stable L-form S. typhimurium induced gamma delta T cells in the liver, in accordance with the multiplication of L-form Salmonella in Kupffer cells. The number of gamma delta T cells decreased after the intracellular growth of L-form Salmonella plateaued. Persistance of the L-forms in Kupffer cells, however, allowed hepatic gamma delta T cells to increase within 48 hr of infection with virulent S. typhimurium. Thus, the intrahepatic colonization of L-form Salmonella seems to keep gamma delta T cells on standby, but the emergence of these T cells does not correlate with the expression of L-form hsp. In addition, Kupffer cells colonized by L-forms constitutively synthesized mRNA for interleukin-6 (IL-6) and tumour necrosis factor-alpha (TNF-alpha). These results suggest that conversion of S. typhimurium to L-forms in phagocytic cells builds up and maintains acquired resistance, conferred by live-cell vaccines of S. typhimurium, against murine typhoid.

Direct presentation of nonpeptide prenyl pyrophosphate antigens to human gamma delta T cells

Human V gamma 2V delta 2+ T cells recognize mycobacterial nonpeptide antigens, such as isopentenyl pyrophosphate, and their synthetic analogs, such as monoethyl phosphate, through a TCR-dependent process. Here, we examine the presentation of these antigens. V gamma 2V delta 2+ T cells recognized secreted prenyl pyrophosphate antigens in the absence of other accessory cells but, under such conditions, required T cell-T cell contact. Recognition required neither the expression of classical MHC class I, MHC class II, or CD1a, CD1b, and CD1c molecules, nor MHC class I or class II peptide loading pathways. Fixed accessory cells also presented the prenyl pyrophosphate antigens to gamma delta T cells. Thus, in contrast with the presentation of conventional peptide antigens, protein antigens, and superantigens to alpha beta T cells, prenyl pyrophosphate antigens are presented to gamma delta T cells through a novel extracellular pathway that does not require antigen uptake, antigen processing, or MHC class I or class II expression. This pathway allows for the rapid recognition of bacteria by gamma delta T cells and suggests that gamma delta T cells play a role in the early response to bacterial infection.

Bacterial superantigens induce the proliferation of resting gamma/delta receptor bearing T cells

We observe that highly purified (> or = 97% pure) gamma/delta T cells isolated from normal peripheral blood proliferate to bacterial toxin supperantigens SEA, SEB, SED, and TSST-1. MHC class II molecules were necessary and sufficient for the recognition of superantigens by gamma/delta T cells because MHC Class II deficient B cell line failed to support the proliferation of gamma/delta T cells to toxins and murine L cells transfected with HLA-DR but not untransfected cells were capable of presenting toxins to gamma/delta T cells. As in the case with alpha/beta T cells, bacterial superantigens synergized with PMA in causing the proliferation of purified gamma/delta T cells rigorously depleted of accessory cells. Together, our findings suggest that gamma/delta T cells recognize and respond to bacterial superantigens in a manner similar to alpha/beta T cells.

Current perspectives in salmonellosis

Salmonellosis remains an important human and animal problem worldwide and, despite extensive research effort, many of the details of its pathogenesis are not known. While there have been recent advances in some aspects of pathogenesis, other areas are not understood. The host adaptation shown by several serotypes and the recent dramatic changes in the predominance of particular serotypes are examples. Molecular techniques using in vitro model systems have identified several genes involved in adhesion and invasion, though their function and even their relevance to disease remain poorly defined. Similarly, several potential toxins have been identified and the genes cloned, although their significance is far from clear. Some of the essential genes on the large virulence plasmids have been defined, and these are known to be necessary for the establishment of systemic infection. Two of these genes are regulatory, but the function of the other genes is unknown. A general theme has been the identification of gene systems involved in regulation of virulence. New vaccines, based on 'rational attenuation' are being designed, and these have also been used to carry heterologous antigens; such vaccines are currently undergoing trials. The improved understanding of the pathogenesis of salmonellosis may also provide a model of wide applicability to a more general understanding of bacterial pathogenesis. New techniques, including the polymerase chain reaction, are being applied to diagnose salmonellosis.

Effects of in vivo administration of anti-IL-10 monoclonal antibody on the host defence mechanism against murine Salmonella infection

Interleukin-10 (IL-10) is a cytokine that regulates various macrophage functions. To elucidate the involvement of endogenous IL-10 in the early stage of murine salmonellosis, we examined the effect of anti-IL-10 monoclonal antibody (mAb) administration on the host defence mechanism against Salmonella choleraesuis infection. The in vivo administration of anti-IL-10 mAb significantly enhanced host resistance at the early stage of Salmonella infection, as assessed by bacterial growth in the peritoneal cavity and the liver. Enhanced levels of monokine mRNA, including IL-1 alpha, tumour necrosis factor-alpha (TNF-alpha) and IL-12, were observed from day 1 after infection in the peritoneal macrophages in anti-IL-10 mAb-treated mice compared with those in control mAb-treated mice. Mice treated with anti-IL-10 mAb exhibited significantly higher levels of interferon-gamma (IFN-gamma) in the peritoneal exudates and major histocompatibility complex (MHC) class II expression on the peritoneal macrophages on days 3 and 5 after infection. Notably, in vivo anti-IL-10 mAb brought about an increment of gamma delta T cells in the peritoneal cavity at the early phase of infection, which was correlated with the expression of endogenous heat-shock protein 60 (HSP60), which is implicated as a potential ligand for gamma delta T cells, in the infected macrophages. Our results suggest that the neutralization of endogenous IL-10 accelerates some macrophage functions and, consequently, the activation of immunocompetent cells, including gamma delta T cells, at the early stage of infection, resulting in an enhanced host defence against Salmonella infection.

The role of gamma delta T cells in priming macrophages to produce tumor necrosis factor-alpha

The secretion of tumor necrosis factor (TNF)-alpha from macrophages is regulated by both priming and triggering signals. We found that macrophages from mice lacking gamma delta T cells [T cell receptor (TCR) delta-/- mice], which lack the gene encoding the delta chain, produced only small amounts of TNF-alpha in response to lipopolysaccharide (LPS) and showed a reduced level of expression of CD14. Pre-incubation of macrophages from TCR delta-/- mice with gamma delta T cells from their TCR delta +/- littermates restored their capacity to produce TNF-alpha in response to LPS. The priming activity of gamma delta T cells was in part inhibited by neutralizing anti-interferon (IFN)-gamma monoclonal antibodies. Collectively, these results suggest that gamma delta T cells play a role in priming macrophages to a steady state of activation via IFN-gamma secretion, which allows them to produce TNF-alpha when exposed to LPS.

The role of CD4+ and CD8+ T cells in protective immunity to the murine nematode parasite Trichuris muris

The role of CD4+ and CD8+ T cells in protective immunity to Trichuris muris was studied in CD4+ or CD8+ or both CD4+ and CD8+ T cell-depleted BALB/c mice. To assess in vivo depletion of T-cell subsets, CD4+ and CD8+ T cells in the Peyer's patches, the mesenteric lymph nodes (MLN), and the spleens of mice treated with T cell-specific monoclonal antibodies (MoAbs) were analysed by FACS. CD4+ T cells were selectively depleted in mice injected with anti-CD4 MoAb i.p. and injection of anti-CD8 MoAb resulted in selective depletion of CD8+ T cells. The expulsion of T. muris was inhibited in CD4+ T cell-depleted mice and numerous worms were detected in the large intestine on days 14 and 21 after infection, although no suppression of protective immunity to T. muris was observed in CD8+ T cell-depleted mice. Moreover, there was no difference in suppression of protective immunity to T. muris between CD4+ T cell-depleted and both CD4+ and CD8+ T cells play a central role in protective immunity to T. muris infection.

Interaction between gamma delta T cells and B cells regulating IgG production

Despite profound knowledge about the molecular structure of the gamma delta T-cell receptor (TCR), the physiological function of gamma delta T cells remains enigmatic. Participation of these cells in complex immune reactions, however, is suggested by the appearance of gamma delta T cells in sites of infectious and autoimmune-induced inflammations. Only a few in vitro models of gamma delta T-cell stimulation have been established: besides a reactivity in the presence of microbial ligands, human gamma delta T cells proliferate upon in vitro challenge with cells from an allogeneic B-lymphoblastic cell line (B-LCL). We present data here demonstrating that this reactivity is not confined to allogenic B-LCL. Autologous B-LCL are also very strong stimulators for gamma delta T cells; more important, autologous B cells can stimulate gamma delta T cells after a period of mitogen-activation but not in a resting state. This activation seems to address a subgroup of gamma delta T cells, as the percentage of V delta 1+ cells is increased after stimulation. Activated gamma delta T cells, on the other hand, are able to exert an influence on B cells by inhibiting the secretion of IgG in coculture experiments. These data define a simple regulatory circle of B cells and gamma delta T cells in vitro and propose a model for gamma delta T-cell function which could explain many in vivo observations of gamma delta T-cell activation.

Characterization of a 10- to 14-kilodalton protease-sensitive Mycobacterium tuberculosis H37Ra antigen that stimulates human gamma delta T cells

gamma delta T-cell receptor-bearing T cells (gamma delta T cells) are readily activated by intracellular bacterial pathogens such as Mycobacterium tuberculosis. The bacterial antigens responsible for gamma delta T-cell activation remain poorly characterized. We have found that heat treatment of live M. tuberculosis bacilli released into the supernatant an antigen which stimulated human gamma delta T cells. gamma delta T-cell activation was measured by determining the increase in percentage of gamma delta T cells by flow cytometry in peripheral blood mononuclear cells stimulated with antigen and by proliferation of gamma delta T-cell lines with monocytes as antigen-presenting cells. Supernatant from heat-treated M. tuberculosis was fractionated by fast-performance liquid chromatography (FPLC) on a Superose 12 column. Maximal gamma delta T-cell activation was measured for a fraction of 10 to 14 kDa. Separation of the supernatant by preparative isoelectric focusing demonstrated peak activity at a pI of < 4.0. On two-dimensional gel electrophoresis, the 10- to 14-kDa FPLC fraction contained at least seven distinct molecules, of which two had a pI of < 4.5. Protease treatment reduced the bioactivity of the 10- to 14-kDa FPLC fraction for both resting and activated gamma delta T cells. Murine antibodies raised to the 10- to 14-kDa fraction reacted by enzyme-linked immunosorbent assay with antigens of 10 to 14 kDa in lysate of M. tuberculosis. In addition, gamma delta T cells proliferated in response to an antigen of 10 to 14 kDa present in M. tuberculosis lysate. gamma delta T-cell-stimulating antigen was not found in culture filtrate of M. tuberculosis but was associated with the bacterial pellet and lysate of M. tuberculosis. These results provide a preliminary characterization of a 10- to 14-kDa, cell-associated, heat-stable, low-pI protein antigen of M. tuberculosis which is a major stimulus for human gamma delta T cells.

gamma delta T cells play a crucial role in the expression of 65,000 MW heat-shock protein in mice immunized with Toxoplasma antigen

Toxoplasma gondii is an obligate intracellular protozoan parasite and cellular immunity plays a crucial role in protection against infection with this pathogen. When mice are immunized with Toxoplasma homogenate, they readily acquire resistance against infection with a lethal dose of a low virulence Beverley strain of T. gondii. We have reported previously that expression of 65,000 MW heat-shock protein (hsp 65) in host macrophages closely correlates with protective potentials of hosts, while this protein is not expressed in Toxoplasma themselves. In this study, we examined the mechanism of expression of hsp 65 in mice immunized with Toxoplasma homogenate. Heat-shock protein was detected in peritoneal macrophages of BALB/c mice immunized 7 days previously by electroblot assay with a specific monoclonal antibody (mAb) for microbial hsp 65. Furthermore, an immunogold ultracytochemistry assay demonstrated that this protein was expressed on the cell surface of peritoneal macrophages in immune mice. This expression was not induced in those of immune athymic nude mice and SCID mice. Treatment of BALB/c mice with anti-Thy-1.2 mAb 1 day before immunization led to an almost complete loss of the expression of hsp 65. To determine the subsets of T cells responsible for induction of this protein, mice were depleted of gamma delta T cells, alpha beta T cells, CD4+ T cells or CD8+ T cells by treating with corresponding antibodies before immunization. From these experiments, gamma delta T cells were shown to be essential for the expression of hsp 65, although CD4+ alpha beta T cells also contributed to some extent. Thus, gamma delta T cells appear to play an important role in protective immunity against infection with T. gondii through mediating the expression of hsp 65 in host macrophages.

The Salmonella typhimurium katF (rpoS) gene: cloning, nucleotide sequence, and regulation of spvR and spvABCD virulence plasmid genes

The spv region of Salmonella virulence plasmids is essential for the development of a systemic infection in mice. Transcriptional activation of the spvABCD operon occurs during stationary growth phase and is mediated by the regulatory gene product SpvR. We have previously shown that expression of a spvRAB'-cat fusion in Escherichia coli was dependent on the katF (rpoS) locus which encodes an alternative sigma factor (sigma S). The katF gene from Salmonella typhimurium has been cloned, sequenced, and used to construct Salmonella katF mutants by allelic replacement. Using these mutants, we demonstrated by mRNA and gene fusion analyses that sigma S, in conjunction with SpvR, controls the transcription of the regulatory gene spvR. In a second series of experiments, we sought to clarify the relationship between sigma S and SpvR in the control of spvABCD transcription. It was shown that expression of a transcriptional spvAB'-lacZ fusion could be restored in E. coli and Salmonella katF mutants when spvR was expressed in trans from an exogenous promoter. Moreover, identical spvA mRNA startpoints were detected in katF+ and katF strains. These results indicate that the reduction of spvABCD transcription in katF mutants is mainly due to decreased expression of spvR. Finally, mouse inoculation studies with S. typhimurium katF mutants of both wild-type and virulence plasmid-cured strains suggest that katF contributes to Salmonella virulence via the regulation of chromosomal genes in addition to that of spv genes.

Mouse T lymphocytes that express a gamma delta T-cell antigen receptor contribute to resistance to Salmonella infection in vivo

Mice depleted of lymphocytes expressing the alpha beta or the gamma delta T-cell receptor for antigen (TCR) by antibody treatment were infected orally with Salmonella enteritidis. In both groups of treated mice, the 50% lethal dose decreased, suggesting that both the alpha beta TCR+ and the gamma delta TCR+ subsets contribute to resistance to oral infection. These data provide further evidence for the contribution of gamma delta T cells in the response to bacterial infections.

Protective role for heat shock protein-reactive alpha beta T cells in murine yersiniosis

To investigate the role of heat shock proteins (HSP) of Yersinia enterocolitica for the host immune response against this pathogen, we cloned and expressed a 60-kDa HSP of Y. enterocolitica serotype O8. A fragment of Y. enterocolitica O8 HSP60 encoded by amino acids 90 to 286 was sequenced and showed more than 90% homology with HSP60 of Y. enterocolitica O3 and GroEL of Escherichia coli and 59% homology with HSP65 of Mycobacterium bovis. The arthritogenic T-cell epitope of mycobacterial HSP65 (amino acid residues 180 to 188) was not found on Yersinia HSP60. To determine whether Yersinia HSP60 is an immunodominant antigen, the immune responses of Yersinia-infected C57BL/6 mice were analyzed. Yersinia-infected mice evolved a significant serum antibody and splenic T-cell response against Yersinia HSP60. CD4+ alpha beta T-cell clones which were generated from splenic T cells isolated from either Yersinia-infected or Yersinia HSP60-immunized mice, recognized both heat-killed Yersinia serotypes O3 and O8 as well as recombinant Yersinia HSP60 but not heat-killed Yersinia pseudotuberculosis, Salmonella typhimurium, or recombinant HSP65 of Mycobacterium bovis. The adoptive transfer of HSP60-reactive T-cell clones mediated significant protection against a lethal infection with Y. enterocolitica O8. These results indicate that HSP60 of Y. enterocolitica is an immunodominant antigen which is recognized by both antibodies and CD4+ alpha beta T cells. Moreover, this is the first report providing direct evidence that microbial HSP may elicit a protective immune response which is not associated with autoimmunity.

Sendai virus pneumonia: evidence for the early recruitment of gamma delta T cells during the disease course

We previously reported that gamma delta T cells appeared and could play a protective role early in infections with intracellular bacteria such as Listeria monocytogenes, Mycobacterium bovis BCG, and Salmonella choleraesuis. To extend these findings to virus infection, we examined the developmental sequence of gamma delta T cells in bronchoalveolar lavage during the course of Sendai virus infection in C57BL/6 mice. To produce a natural but nonlethal infection course as far as possible, we used a sublethal dose of a wild-type virus which had not been subjected to serial passages in a chicken embryo, hence retaining full virulence for mice. Virus titers in lungs reached a peak on day 6 and then decreased to an undetectable level by day 10. This time course of virus reproduction was immediately and coincidentally followed by the developmental course of gamma delta T cells, in which the cell number peaked on day 7 and then decreased to a marginal level by day 10. On the other hand, the alpha beta T-cell number continued to increase until day 10 and remained at a high level thereafter. The early-appearing gamma delta T cells were CD4-, CD8-, IL-2R alpha- beta+, CD44+, Mel-14-, and LFA-1 alpha/beta+ in phenotype and used V gamma 1/2 and V gamma 4 and V delta 3, V delta 4, V delta 5, and V delta 6. The gamma delta T cells were responding to macrophages from infected mice when the cells were cultured in vitro. Furthermore, the expression of endogenous heat shock protein (hsp) was infection specific, and its level appeared to correlate with the gamma delta T-cell development. These results suggest that the early recruitment of gamma delta T cells, which proliferate in response to endogenous hsp+ cells, is also characteristic of this virus infection, although this view appears to be contradictory to earlier reports.

Augmentation of the resistance against Listeria monocytogenes by oral administration of a hot water extract of Chlorella vulgaris in mice

Oral administration of a hot water extract of Chlorella vulgaris(CVE)(20mg/mouse, 10 consecutive days) augmented the resistance against an i.p. infection with Listeria monocytogenes in mice. The numbers of bacteria in a CVE-administered group were significantly lower in the peritoneal cavity or spleen than those in a control group. FCM analysis revealed that gamma delta +Thy1.2+ cells in the nonadherent PEC from CVE-administered mice increased more prominently in number at the early stage on day 3 or on day 5 after infection as compared with those in control mice. The increment of gamma delta +Thy1.2+ T cells was also evident in spleen in CVE-administered mice at this stage after infection. The proportion of TCR alpha beta +Thy1.2+ T cells in the nonadherent PEC of a control group increased from 13% on day 0 to 49% at the late stage on day 10 after infection, whereas the proportion of TCR alpha beta +Thy1.2+ T cells in the nonadherent PEC in CVE-administered mice increased to 64% on this stage after infection in association with augmentation of DTH response to Listeria. These results suggest that CVE-administration effectively augment cell-mediated immunity against Listeria through the increment of gamma delta + T cells in the early phase and the increment of alpha beta + T cells in the late phase after listerial infection.

Polyclonal expansion of peripheral gamma delta T cells in human Plasmodium falciparum malaria

Plasmodium falciparum malaria in humans is associated with an increase in the percentage and absolute number of gamma delta T cells in the peripheral blood. This increase begins during the acute infection phase and persists for at least 4 weeks during convalescence. In the present study, 25 to 30% of the gamma delta T cells expressed HLA-DR antigens in vivo and in some patients they proliferated in response to further stimulation by purified human interleukin 2 in vitro. However, there was no in vitro proliferative response to various malarial antigens, including a 75-kDa heat shock protein and a 72-kDa glucose-regulated protein of P. falciparum during the acute infection phase. Cytofluorographic studies showed that although an increase of V delta 1- gamma delta T cells was largely responsible for the expansion of the total number of gamma delta T cells, there was also a proportional increase in V delta 1+ cells. These results were confirmed with anchored PCR and by DNA sequencing to characterize at the molecular level the set of T-cell receptor (TCR) delta mRNAs expressed in the peripheral blood of two patients with high levels of gamma delta T cells. In each case, most of the TCR delta mRNA transcripts corresponded to nonproductively rearranged delta genes (unrearranged J delta or near J delta spliced to C delta). In those sequences which did represent productively rearranged genes, most of the transcripts originated from a V delta 2/J delta 1 joining, as in normal individuals. A minority of transcripts originated from a V delta 1/J delta 1 rearrangement, and one originated from a V alpha 4/J delta 1 rearrangement. Polyclonal activation of gamma delta T cells was inferred from the extensive junctional diversity seen in the delta mRNAs analyzed. Expansion of a heterogeneous set of both V delta 1(-)- and V delta 1(+)-bearing T cells suggests that the elevated levels of gamma delta T cells seen during acute P. falciparum malaria arose from immune responses to multiple distinct parasite antigens or unidentified host factors.

Antigens recognized by gamma delta T cells

Recent evidence demonstrates the important role played by gamma delta T cells in resistance to infections. Despite this, in most cases the antigens recognized by the responding gamma delta T cells are unknown. Antigen recognition by some gamma delta T-cell populations may not require the participation of either MHC class I or class II molecules. In other cases, evidence exists for the participation of MHC-encoded molecules, particularly non-classical class I molecules.

A protective role of extrathymic alpha beta TcR cells in the liver in primary murine salmonellosis

The liver comprises unique T cells differentiating extrathymically and expressing an intermediate intensity of alpha beta T-cell receptor (TcR) and a high intensity of leucocyte function antigen-1 (LFA-1). To elucidate the functional roles of the intermediate alpha beta TcR cells in host defence against bacterial infection, we examined the effects of depletion of the intermediate alpha beta TcR cells by in vivo administration of monoclonal antibodies (mAb) to intercellular adhesion molecule-1 (ICAM-1)/LFA-1 and alpha beta TcR on the bacterial growth in the liver after infection with Salmonella chorelaesuis in mice. Pretreatment with mAb to LFA-1 (200 micrograms/mouse) together with mAb to ICAM-1 (200 micrograms/mouse), which could preferentially deplete the intermediate alpha beta TcR cells and gamma delta TcR cells in the liver, resulted in a severely reduced ability to resolve acute phase of Salmonella infection in the liver. Pretreatment with a low dose of anti-alpha beta TcR mAb (60 micrograms/mouse), which depleted only bright alpha beta TcR cells, did not affect the bacterial growth in the liver at the early stage after Salmonella infection, while the depleting of both intermediate and bright alpha beta TcR cells by pretreatment with a high dose of anti-alpha beta TcR mAb (120 micrograms/mouse) allowed the bacteria to multiply exaggeratedly in the liver at this stage. These results suggest that intermediate alpha beta TcR cells may play an important role in protection at the early stage after Salmonella infection in liver and that the interaction of ICAM-1/LFA-1 is critically involved in protective roles of extrathymic T cells bearing intermediate alpha beta TcR in liver at the early stage after Salmonella infection.

Dynamic response of murine gut intraepithelial T cells after infection by the coccidian parasite Eimeria

The response of murine intraepithelial lymphocyte (IEL) populations to challenge by Eimeria vermiformis, a naturally occurring protozoan parasite of the gut epithelium, has been studied. The number of recoverable IEL increased within 3 days post infection, was depleted by day 7 post infection, but was significantly increased again by about day 14 post infection. Special attention was paid to gamma delta+ IEL T cells, because they are of unknown functions. These cells showed changes in numbers similar to the total IEL population. Moreover, by day 3, increased expression was detected among gamma delta+ IEL T cells, of T cell receptor genes not constitutively associated with the intestine. These results demonstrate that the IEL repertoire, and within that, the gamma delta+ T cell repertoire, can be extremely dynamic post infection with a naturally occurring epithelial-tropic pathogen. In considering the potential benefits of such IEL changes, we hypothesize that they may be relevant to the transient protection of the host's epithelium, both from parasitic re-infection, and from potentially damaging inflammation.

Lymphocytes bearing the gamma delta T cell receptor in acute Brucella melitensis infection

A phenotypical analysis carried out by indirect immunofluorescence and two-color cytofluorometry showed that the number of lymphocytes bearing the gamma delta T cell receptor (TcR) heterodimer was dramatically increased in the blood of six children with Brucella melitensis infection. Most in vivo expanded gamma delta T cells reacted with a monoclonal antibody which identifies V delta 2 gene products and a significant proportion expressed CD25 and HLA-DR activation antigens. In addition, whereas only a few gamma delta T lymphocytes were CD8+, nearly all were CD4-. Highly enriched populations of both alpha beta and gamma delta T cells were obtained by negative immunoselection from three subjects with brucellosis sampled during convalescence. Despite the different form of their TcR, the proliferation of these two major T cell subsets in response to a mitogenic anti-CD3 monoclonal reagent (OKT3) was optimal. In contrast, alpha beta, but not gamma delta, T lymphocytes proliferated vigorously in response to the antigenic stimulus elicited by heat-killed Brucella. Further studies are, therefore, needed to determine whether the selective expansion of the gamma delta T cell subpopulation observed during the clinical course of the infection is driven by antigenic determinant(s) borne by the pathogen in vivo or is due to host-derived stimuli, such as autologous heat-shock proteins expressed on the surface of the infected cells.

Molecular analysis of spv virulence genes of the Salmonella virulence plasmids

Genes on an 8 kb region common to the virulence plasmids of several serovars of Salmonella are sufficient to replace the entire plasmid in enabling systemic infection in animal models. This virulence region encompasses five genes which previously have been designated with different names from each investigating laboratory. A common nomenclature has been devised for the five genes, i.e. spv for salmonella plasmid virulence. The first gene, spvR, encodes a positive activator for the following four genes, spvABCD. DNA sequence analysis of the spv genes from Salmonella typhimurium, Salmonella dublin, and Salmonella choleraesuis demonstrated extremely high conservation of the DNA and amino acid sequences. The spv genes are induced at stationary phase and in carbon-poor media, and optimal expression is dependent on the katF locus. The virulence functions of the spv genes are not known, but these genes may increase the growth rate of salmonellae in host cells and affect the interaction of salmonellae with the host immune system.

The Salmonella typhimurium virulence plasmid increases the growth rate of salmonellae in mice

The virulence plasmids of Salmonella typhimurium and other invasive Salmonella serovars have long been associated with the ability of these bacteria to cause systemic infection beyond the intestines in orally inoculated animals. Genetic analysis of virulence genes on the high-molecular-weight plasmids has revealed that no more than five genes spanning a 6.2-kb region are sufficient to replace the entire plasmid for conferring virulence. However, the exact virulence function(s) encoded by these genes has not been elucidated. In this report, we measured the possible effect of the virulence plasmid on the growth rate of S. typhimurium in mice by two complementary procedures. The first procedure used segregation of a temperature-sensitive plasmid in vivo to provide a measure of bacterial divisions and the number of recovered marker plasmid-containing salmonellae as a measure of killing. In the second procedure, aroA deletions were transduced into virulence plasmid-containing and plasmid-cured S. typhimurium. Since AroA- salmonellae are inhibited for growth in vivo, if the virulence plasmid affected only growth rate, no difference in the recoveries of the paired AroA- strains would be seen. Virulence plasmid-containing S. typhimurium segregated the marker plasmid more rapidly than did the virulence plasmid-cured strain, and AroA- derivatives of both strains were recovered equally from mice. Therefore, the S. typhimurium virulence plasmid increased growth rate but had no detectable effect on killing or bacterial movement into deep tissues. To examine whether the plasmid accomplished this function by affecting the intracellular/extracellular location of bacteria, orally infected mice were injected with gentamicin to kill the extracellular bacteria. Wild-type and plasmid-cured S. typhimurium strains were equally resistant to gentamicin in vivo and hence most likely located intracellularly to equal degrees. When wild-type and plasmid-cured S. typhimurium strains were sequestered within peritoneal chambers in mice, the resulting extracellular growth was equal. Therefore, the virulence plasmid increases the growth rate of S. typhimurium in mice, probably within mouse cells.