Functional analysis of DR17(DR3)-restricted mycobacterial T cell epitopes reveals DR17-binding motif and enables the design of allele-specific competitor peptides

We have previously shown that p3-13 (KTIAY-DEEARR) of the 65-kDa heat shock protein (hsp65) of Mycobacterium tuberculosis and Mycobacterium leprae is selected as an important T cell epitope in HLA-DR17+ individuals, by selectively binding to (a pocket in) DR17 molecules, the major subset of the DR3 specificity. We have now further studied the interaction between p3-13, HLA-DR17 and four different TCR (V beta 5.1, V beta 1, and V beta 4) by using T cell stimulation assays, direct peptide-DR binding assays, and a large panel (n = 240) of single amino acid substitution analogs of p3-13. We find that residues 5(I) and 8(D) of p3-13 are important DR17 binding residues, whereas the residues that interact with the TCR vary slightly for each DR17-restricted clone. By using N- and C-terminal truncated derivatives of p2-20 we defined the minimal peptide length for both HLA-DR17 binding and T cell activation: the minimal peptide that bound to DR17 was seven amino acids long whereas the minimal peptide that activated T cell proliferation was eight amino acids in length. Furthermore, two new DR17-restricted epitopes were identified on hsp70 and hsp18 of M. leprae. Alignment of the critical DR17-binding residues 5(I) and 8(D) of p3-13 with these two novel epitopes and two other DR17-binding peptides revealed the presence of highly conserved amino acids at positions n and n + 3 with I, L, and V at position n and D and E at position n + 3. D and E are particularly likely to interact with the DR17-specific, positively charged pocket that we have defined earlier. Based on these results, a set of single amino acid substituted analogs that failed to activate these T cell clones but still bound specifically to DR17 was defined and tested for their ability to inhibit T cell activation by p3-13 or other DR17-restricted epitopes. Those peptides were able to inhibit the response to p3-13 as well as other DR17-restricted mycobacterial epitopes in an allele-specific manner, and are anticipated to be of potential use for immunotherapeutic and vaccine design strategies.

Functional analysis of DR17(DR3)-restricted mycobacterial T cell epitopes reveals DR17-binding motif and enables the design of allele-specific competitor peptides

We have previously shown that p3-13 (KTIAY-DEEARR) of the 65-kDa heat shock protein (hsp65) of Mycobacterium tuberculosis and Mycobacterium leprae is selected as an important T cell epitope in HLA-DR17+ individuals, by selectively binding to (a pocket in) DR17 molecules, the major subset of the DR3 specificity. We have now further studied the interaction between p3-13, HLA-DR17 and four different TCR (V beta 5.1, V beta 1, and V beta 4) by using T cell stimulation assays, direct peptide-DR binding assays, and a large panel (n = 240) of single amino acid substitution analogs of p3-13. We find that residues 5(I) and 8(D) of p3-13 are important DR17 binding residues, whereas the residues that interact with the TCR vary slightly for each DR17-restricted clone. By using N- and C-terminal truncated derivatives of p2-20 we defined the minimal peptide length for both HLA-DR17 binding and T cell activation: the minimal peptide that bound to DR17 was seven amino acids long whereas the minimal peptide that activated T cell proliferation was eight amino acids in length. Furthermore, two new DR17-restricted epitopes were identified on hsp70 and hsp18 of M. leprae. Alignment of the critical DR17-binding residues 5(I) and 8(D) of p3-13 with these two novel epitopes and two other DR17-binding peptides revealed the presence of highly conserved amino acids at positions n and n + 3 with I, L, and V at position n and D and E at position n + 3. D and E are particularly likely to interact with the DR17-specific, positively charged pocket that we have defined earlier. Based on these results, a set of single amino acid substituted analogs that failed to activate these T cell clones but still bound specifically to DR17 was defined and tested for their ability to inhibit T cell activation by p3-13 or other DR17-restricted epitopes. Those peptides were able to inhibit the response to p3-13 as well as other DR17-restricted mycobacterial epitopes in an allele-specific manner, and are anticipated to be of potential use for immunotherapeutic and vaccine design strategies.

First International Conference on the Pathogenesis of Mycobacterial Infections: a summary

Two hundred scientists representing 25 countries assembled for the First International Conference on the Pathogenesis of Mycobacterial Infections, which was held in Stockholm on 27-29 June 1990. A total of 40 speeches and 80 poster presentations covered nearly all of the recent progress made in the field of mycobacterial pathogenicity. The present report is intended as a brief summary of the research results presented during the conference and focuses on findings of broad scientific interest. However, the omission of other presented findings from this report does not constitute any judgment of their scientific quality.

High-efficiency expression and solubilization of functional T cell antigen receptor heterodimers

The T cell receptor (TCR) zeta chain was attached to the TCR alpha and beta extracellular domains to induce efficient expression of alpha beta heterodimers that can recognize complexes of antigen with major histocompatibility complex (MHC) molecules. Chimeric constructs expressed in RBL-2H3 cells were efficiently transported to the cell surface uniquely as disulfide-linked heterodimers. Transfectants were activated by specific antigen-MHC complexes, which demonstrated that the expressed alpha beta was functional and that CD3 was not required for antigen-MHC binding. Constructs with thrombin cleavage sites were efficiently cleaved to soluble disulfide-linked heterodimers. Thus, attachment of TCR zeta domains and protease cleavage sites to TCR alpha and beta induces expression of demonstrably functional heterodimers that can be solubilized.

Binding of a major T cell epitope of mycobacteria to a specific pocket within HLA-DRw17(DR3) molecules

CD4+ T cells recognize antigenic peptides bound to the polymorphic peptide-binding site of major histocompatibility complex (MHC) class II molecules. The polymorphism of this site is thought to dictate which peptides can be bound and thus presented to the T cell receptor. The mycobacterial 65-kDa heat-shock protein (hsp65) peptide 3-13 is an important T cell epitope: it is immunodominant in the mycobacterium-specific T cell response of HLA-DR3+ individuals but, interestingly cannot be recognized in the context of any other HLA-DR molecules. We, therefore, have tested whether the hsp65 epitope p3-13 is selected for T cell recognition in the context of only HLA-DR3 molecules by an unique binding specificity for HLA-DR3. Using biotinylated peptides and EBV-transformed BLCL comprising all known HLA class II specificities, we find that p3-13 binds to HLA-DRw17(DR3) but not to any other HLA-DR molecule. Conversely, a control peptide p307-319 influenza hemagglutinin binds to all known HLA-DR molecules but only weakly to HLA-DRw17 and HLA-DR9. Peptide binding could be inhibited by excess unbiotinylated competitor analogue as well as by anti-DR monoclonal antibodies but not by anti-class I-, anti-DP- or anti-DQ monoclonal antibodies. The amino acid sequence of DRw17 molecules differs uniquely at five positions from the other DR beta 1 sequences. Three of these five residues (positions 26, 71 and 74) are potential peptide contacting residues. These residues map closely together in the hypothetical three-dimensional model of the DR molecule and, thus, most probably form a positively charged pocket, critical for the binding of p3-13. Interestingly, p3-13 does not bind to a DR3 variant, the DRw18 molecule. The DRw18 beta 1 chain differs from DRw17 at two major positions, close to or within the DRw17-specific pocket. These substitutions drastically change the structure and charge of the pocket and thus presumably abrogate its ability to bind p3-13.

Molecular and immunological analysis of a fibronectin-binding protein antigen secreted by Mycobacterium leprae

By screening a Mycobacterium leprae lambda gt11 genomic DNA library with leprosy-patient sera we have previously identified 50 recombinant clones that expressed novel M. leprae antigens (Sathish et al., 1990). In this study, we show by DNA sequencing and immunoblot analysis that three of these clones express a M. leprae homologue of the fibronectin-binding antigen 85 complex of mycobacteria. The complete gene was characterized and it encodes a 327-amino-acid polypeptide, consisting of a consensus signal sequence of 38 amino acids followed by a mature protein of 289 amino acids. This is the first sequence of a member of the M. leprae antigen 85 complex, and Southern blotting analysis indicated the presence of multiple genes of the 85 complex in the genome of M. leprae. The amino acid sequence displays 75-85% sequence identity with components of the antigen 85 complex from M. tuberculosis, M. bovis BCG and M. kansasii. Furthermore, antibodies to the antigen 85 complex of M. tuberculosis and M. bovis BCG reacted with two fusion proteins containing the amino acid regions 55-266 and 266-327 of the M. leprae protein. The M. leprae 30/31 kDa protein induces strong humoral and cellular responses, as judged by Western blot analysis with patient sera and proliferation of T cells derived from healthy individuals and leprosy patients. Amino acid regions 55-266 and 265-327 both were shown to bind to fibronectin, indicating the presence of at least two fibronectin-binding sites on the M. leprae protein. These data indicate that this 30/31 kDa protein is not only important in the immune response against M. leprae, but may also have a biological role in the interaction of this bacillus with the human host.

A systematic molecular analysis of the T cell-stimulating antigens from Mycobacterium leprae with T cell clones of leprosy patients. Identification of a novel M. leprae HSP 70 fragment by M. leprae-specific T cells

Both protective immunity and immunopathology induced by mycobacteria are dependent on Ag-specific, CD4+ MHC class II-restricted T lymphocytes. The identification of Ag recognized by T cells is fundamental to the understanding of protective and pathologic immunity as well as to the design of effective immunoprophylaxis and immunotherapy strategies. Although some T cell clones are known to respond to recombinant mycobacterial heat shock proteins (hsp) like hsp3 65, the specificity of most T cells has remained unknown. We therefore have undertaken a specificity analysis of 48 well defined Mycobacterium leprae- and/or Mycobacterium tuberculosis-reactive (Th-1-like) T cell clones. Most clones (n = 44) were derived from different leprosy patients, and the remainder from one healthy control. Their HLA restriction molecules were DR2, DR3, DR4, DR5, DR7, DQ, or DP. T cell clones were stimulated with large numbers (n = 20 to 40) of mycobacterial SDS-PAGE-separated fractions bound to nitrocellulose. Each clone recognized a single fraction or peak with a particular Mr range. Some of the clones (n = 7) recognized the fraction that contained the hsp 65 as confirmed with the recombinant Ag. Most clones (n = 41), however, responded to Ag other than the hsp 65. Nine clones responded to a 67- to 80-kDa fraction. Five of them responded also to an ATP-purified, 70-kDa M. leprae protein, but only one of these five (that was HLA-DR2 restricted and cross-reactive with M. tuberculosis) recognized the recombinant C-terminal half (amino acids 278-621) of the M. leprae hsp 70 molecule and also recognized the recombinant M. tuberculosis hsp 70. We therefore have used the 5' part of the M. leprae hsp 70 gene that we have cloned recently. This fragment (that encodes amino acids 6-279) was indeed recognized by the other four M. leprae-specific T cells that were all HLA-DR3 restricted and did not cross-react with the highly homologous (95%) M. tuberculosis hsp 70. These results suggest that this novel fragment is a relevant T cell-stimulating Ag for leprosy patients. A panel of other recombinant Ag, including hsp 18 was tested. The majority of T cell clones appeared to recognize antigenic fractions distinct from hsp. In conclusion, T cells of leprosy patients see a large variety of different Ag including non-hsp, and one newly recognized moiety is the N-terminal M. leprae hsp 70 fragment.(ABSTRACT TRUNCATED AT 400 WORDS)

A systematic molecular analysis of the T cell-stimulating antigens from Mycobacterium leprae with T cell clones of leprosy patients. Identification of a novel M. leprae HSP 70 fragment by M. leprae-specific T cells

Both protective immunity and immunopathology induced by mycobacteria are dependent on Ag-specific, CD4+ MHC class II-restricted T lymphocytes. The identification of Ag recognized by T cells is fundamental to the understanding of protective and pathologic immunity as well as to the design of effective immunoprophylaxis and immunotherapy strategies. Although some T cell clones are known to respond to recombinant mycobacterial heat shock proteins (hsp) like hsp3 65, the specificity of most T cells has remained unknown. We therefore have undertaken a specificity analysis of 48 well defined Mycobacterium leprae- and/or Mycobacterium tuberculosis-reactive (Th-1-like) T cell clones. Most clones (n = 44) were derived from different leprosy patients, and the remainder from one healthy control. Their HLA restriction molecules were DR2, DR3, DR4, DR5, DR7, DQ, or DP. T cell clones were stimulated with large numbers (n = 20 to 40) of mycobacterial SDS-PAGE-separated fractions bound to nitrocellulose. Each clone recognized a single fraction or peak with a particular Mr range. Some of the clones (n = 7) recognized the fraction that contained the hsp 65 as confirmed with the recombinant Ag. Most clones (n = 41), however, responded to Ag other than the hsp 65. Nine clones responded to a 67- to 80-kDa fraction. Five of them responded also to an ATP-purified, 70-kDa M. leprae protein, but only one of these five (that was HLA-DR2 restricted and cross-reactive with M. tuberculosis) recognized the recombinant C-terminal half (amino acids 278-621) of the M. leprae hsp 70 molecule and also recognized the recombinant M. tuberculosis hsp 70. We therefore have used the 5' part of the M. leprae hsp 70 gene that we have cloned recently. This fragment (that encodes amino acids 6-279) was indeed recognized by the other four M. leprae-specific T cells that were all HLA-DR3 restricted and did not cross-react with the highly homologous (95%) M. tuberculosis hsp 70. These results suggest that this novel fragment is a relevant T cell-stimulating Ag for leprosy patients. A panel of other recombinant Ag, including hsp 18 was tested. The majority of T cell clones appeared to recognize antigenic fractions distinct from hsp. In conclusion, T cells of leprosy patients see a large variety of different Ag including non-hsp, and one newly recognized moiety is the N-terminal M. leprae hsp 70 fragment.(ABSTRACT TRUNCATED AT 400 WORDS)

Identification of Mycobacterium leprae antigens from a cosmid library: characterization of a 15-kilodalton antigen that is recognized by both the humoral and cellular immune systems in leprosy patients

Screening of the Mycobacterium leprae cosmid library with pooled sera from lepromatous leprosy (LL) patients by a colony immunoblot technique resulted in the identification of about 100 colonies that produced immunologically reactive proteins. Twenty-four of these clones were purified, analyzed, and found to comprise two groups according to the reactivity of the recombinant proteins with LL sera and to the DNA restriction patterns of the recombinant plasmids and cosmids. Proteins specified by clones from group I reacted strongly with LL patients' sera on a Western blot (immunoblot), demonstrating a 15-kDa protein band designated A15. The A15 antigen also reacted with pooled sera from patients with tuberculoid leprosy from the United States and Brazil. Clones from group II did not show any reactive protein band on a Western blot, when reacted with patients' sera. DNAs from cosmids of group II all contain a 10-kb PstI fragment that hybridized to the unique repetitive M. leprae DNA. Sequence analysis of a 1.2-kb fragment containing the entire coding sequence of A15 revealed three open reading frames (ORFs), only one of which (ORF II) contains sufficient genetic information to encode for A15. Part of the A15 gene was found to exist also in a group of lambda gt11:M. leprae clones previously isolated in our laboratory by immunological screening with LL patients' sera. One of the lambda gt11 clones (L8) expresses a beta-galactosidase fusion protein with 89 amino acids from the C terminus of A15. An important result was that the fusion protein was clearly recognized by T cells from leprosy patients. Interestingly, Mycobacterium tuberculosis-stimulated T cells from M. leprae nonresponder (LL as well as borderline tuberculoid) patients were able to respond to the isolated recombinant M. leprae antigen, indicating that nonresponsiveness to M. leprae antigens can be reversible. The sequence of the M. leprae DNA fused to the beta-galactosidase gene of lambda gt11 clone L8 was identical to that of a lambda gt11:M. leprae clone isolated recently that expresses an immunologically reactive fusion protein (S. Laal, Y. D. Sharma, H. K. Prasad, A. Murtaza, S. Singh, S. Tangri, R. Misra, and I. Nath, Proc. Natl. Acad. Sci. USA 88:1054-1058, 1991). Besides the complete sequence of the A15 gene, sequencing data of two flanking ORFs are presented. Downstream from ORF II (A15), ORF III has a high degree of similarity to the genes for tomato ATP-dependent proteases that are members of a larger class of highly conserved proteases ubiquitous among prokaryotes and eukaryotes.(ABSTRACT TRUNCATED AT 400 WORDS)

Selection of a human T helper type 1-like T cell subset by mycobacteria

Mycobacteria elicit a cellular immune response in their hosts. This response usually leads to protective immunity, but may sometimes be accompanied by immunopathology due to delayed type hypersensitivity (DTH). A striking example in man is tuberculoid leprosy, which is characterized by high cellular immunity to Mycobacterium leprae and immunopathology due to DTH. Skin lesions of patients suffering from this disease have the characteristics of DTH reactions in which macrophages and CD4+ T lymphocytes predominate. In animal models, it has been shown that DTH responses are associated with the presence of a particular subset of CD4+ T cells (T helper type 1 [Th1]) that secrete only certain cytokines, such as interleukin 2 (IL-2), interferon gamma (IFN-gamma), and lymphotoxin, but no IL-4 or IL-5. We studied the cytokine release of activated M. leprae-reactive CD4+ T cell clones derived from tuberculoid leprosy patients. These T cell clones, which were reactive with mycobacterial heat shock proteins, exhibited a Th1-like cytokine secretion pattern with very high levels of IFN-gamma. Half of these clones secreted low levels of IL-4 and IL-5, but the ratio of IFN-gamma to IL-4 and IL-5 was much higher than that of T cell clones reactive with nonmycobacterial antigens. A Th1-like cytokine secretion pattern was also observed for T cell clones and polyclonal T cell lines from control individuals that recognized both heat shock and other mycobacterial antigens. The levels of IFN-gamma secreted by these clones were, however, significantly less than those of patient-derived T cell clones. This Th1-like pattern was not found with T cell clones from the same patients and healthy individuals generated in the same manner, but reactive with nonmycobacterial antigens. Our data thus indicate that mycobacteria selectively induce human T cells with a Th1-like cytokine secretion profile.

Mycobacterium leprae-specific T cells from a tuberculoid leprosy patient suppress HLA-DR3-restricted T cell responses to an immunodominant epitope on 65-kDa hsp of mycobacteria

The polar tuberculoid type (TT) of leprosy, characterized by high T cell reactivity to Mycobacterium leprae, is associated with HLA-DR3. Surprisingly, DR3-restricted low T cell responsiveness to M. leprae was found in HLA-DR3-positive TT leprosy patients. This low responsiveness was specifically induced by M. leprae but not by M. tuberculosis and was seen only in patients and not in healthy controls. We studied this patient-specific, M. leprae-induced, DR3-restricted low T cell responsiveness in depth in one representative HLA-DR3-positive TT leprosy patient by using T cell clones. From this patient two types of T cell clones were obtained: one type was cross-reactive with M. tuberculosis and recognized an immunodominant epitope (amino acids 3 to 13) on the 65-kDa heat shock protein (hsp) the other type was M. leprae specific and reacted to a protein other than the 65-kDa one. To examine whether these M. leprae-specific T cell clones were responsible for the DR3-restricted low responsiveness to M. leprae, we tested them for the ability to suppress the proliferation of the DR3-restricted, 65-kDa, hsp-reactive clones. The DR3-restricted, M. leprae-specific T cells completely suppressed the proliferative responses of DR3-restricted, cross-reactive T cell clones to the 65-kDa hsp from the same patient as well as from other individuals. Also, DR3-restricted responses to an irrelevant Ag were suppressed by the M. leprae-specific T cell clones. However, no suppression of non-DR3-restricted T cell responses was seen. Although the mechanism must still be elucidated, this M. leprae-induced, DR3-restricted immunosuppression may at least partly explain the observed DR3-associated low T cell responsiveness in TT leprosy patients.

Mycobacterium leprae-specific T cells from a tuberculoid leprosy patient suppress HLA-DR3-restricted T cell responses to an immunodominant epitope on 65-kDa hsp of mycobacteria

The polar tuberculoid type (TT) of leprosy, characterized by high T cell reactivity to Mycobacterium leprae, is associated with HLA-DR3. Surprisingly, DR3-restricted low T cell responsiveness to M. leprae was found in HLA-DR3-positive TT leprosy patients. This low responsiveness was specifically induced by M. leprae but not by M. tuberculosis and was seen only in patients and not in healthy controls. We studied this patient-specific, M. leprae-induced, DR3-restricted low T cell responsiveness in depth in one representative HLA-DR3-positive TT leprosy patient by using T cell clones. From this patient two types of T cell clones were obtained: one type was cross-reactive with M. tuberculosis and recognized an immunodominant epitope (amino acids 3 to 13) on the 65-kDa heat shock protein (hsp) the other type was M. leprae specific and reacted to a protein other than the 65-kDa one. To examine whether these M. leprae-specific T cell clones were responsible for the DR3-restricted low responsiveness to M. leprae, we tested them for the ability to suppress the proliferation of the DR3-restricted, 65-kDa, hsp-reactive clones. The DR3-restricted, M. leprae-specific T cells completely suppressed the proliferative responses of DR3-restricted, cross-reactive T cell clones to the 65-kDa hsp from the same patient as well as from other individuals. Also, DR3-restricted responses to an irrelevant Ag were suppressed by the M. leprae-specific T cell clones. However, no suppression of non-DR3-restricted T cell responses was seen. Although the mechanism must still be elucidated, this M. leprae-induced, DR3-restricted immunosuppression may at least partly explain the observed DR3-associated low T cell responsiveness in TT leprosy patients.

HLA-DQ molecules and the control of Mycobacterium leprae-specific T cell nonresponsiveness in lepromatous leprosy patients

The major histocompatibility complex (MHC) controls of the outcome of the immune response to T cell-dependent antigens by dictating whether T cell responsiveness will result (MHC-immune response [Ir]genes) or alternatively T cell nonresponsiveness will occur, possibly through the activation of suppressor cells (MHC-immune suppression [Is] genes). In mice, I-A molecules typically restrict antigen-specific helper T cells. In contrast, H-2 I-E molecules have been reported to control nonresponsiveness to a variety of antigens through antigen-specific suppressor cells. In analogy, HLA-DR molecules are the dominant restriction elements for helper T cells in man. This forces the question whether DQ molecules may be involved in controlling nonresponsiveness in man, e.g. through suppression. In one system, T cell nonresponsiveness to Schistosoma japonicum, evidence has been presented supporting this notion. We have now used a second system, Mycobacterium leprae-specific T cell nonresponsiveness, that is typically found in lepromatous leprosy patients. We find positive but limited evidence for a role for HLA-DQ molecules in controlling T cell nonresponsiveness to M. leprae of the 22 nonresponder patients tested, 4 showed a proliferative T cell response to M. leprae after the addition of DQ- but not DR-specific mAb to the cell cultures. In one of the four BCG nonresponders, anti-DQ mAb had a similar effect.

Intradermal recombinant interleukin 2 enhances peripheral blood T-cell responses to mitogen and antigens in patients with lepromatous leprosy

Thirty-one patients with lepromatous leprosy received recombinant interleukin 2 (IL-2) intradermally in doses ranging from 10 to 30 micrograms. Before injection and at time intervals of 2-21 days thereafter, samples of peripheral blood mononuclear cells (PBMC) were obtained. Single or multiple injections (1-3) of IL-2 did not modify the total number of circulating lymphocytes or the number of T cells and the CD4/CD8 T-cell ratio. However, IL-2 had a pronounced influence on the [3H]thymidine incorporation in response to various stimuli 4-8 days after intradermal IL-2. Stimulation indices of three- to sevenfold above pre-IL-2 levels were observed with the polyclonal activator phytohaemagglutinin (PHA) and enhanced thymidine incorporation occurred in the presence of antigens to which the patients were already sensitized, such as purified protein derivative and BCG. IL-2 had no effect on the unresponsive state of lepromatous leprosy patient T cells to the antigens of Mycobacterium leprae.

Specific killing of cytotoxic T cells and antigen-presenting cells by CD4+ cytotoxic T cell clones. A novel potentially immunoregulatory T-T cell interaction in man

Mycobacterial antigens not only stimulate Th cells that produce macrophage-activating factors, but also CD4+ and CD8+ CTL that lyse human macrophages. The mycobacterial recombinant 65-kD hsp was previously found to be an important target antigen for polyclonal CD4+ CTL. Because of the major role of 65-kD hsp in the immune response to mycobacterial as well as autoantigens, we have studied CTL activity to this protein at the clonal level. HLA-DR or HLA-DQ restricted, CD4+CD8- T cell clones that recognize different peptides of the M. leprae 65-kD hsp strongly lysed EBV-BLCL pulsed with specific but not irrelevant peptide. No bystander lysis of B cells, T cells, or tumor cells was seen. Target cell lysis could not be triggered by PMA + Ca2+ ionophore alone and depended on active metabolism. Interestingly, these CD4+ CTL also strongly lysed themselves and other HLA-class II compatible CD4+ (TCR-alpha/beta or -gamma/delta) or CD8+ CTL clones in the presence of peptide, suggesting that CTL are not actively protected from CTL-mediated lysis. Cold target competition experiments suggested that EBV-BLCL targets were more efficiently recognized than CD4+ CTL targets. These results demonstrate that hsp65 peptide-specific HLA class II-restricted CD4+ T cell clones display strong peptide-dependent cytolytic activity towards both APCs, and, unexpectedly, CD4+ and CD8+ CTL clones, including themselves. Since, in contrast to murine T cells human T cells express class II, CTL-mediated T cell killing may represent a novel immunoregulatory pathway in man.

Human suppressor T cell clones lack CD28

Previously we showed that certain T cell lines and clones from a lepromatous leprosy patient displayed a dose-dependent suppression of the proliferation of autologous T cells to Mycobacterium leprae (M. leprae) but not mitogen or an unrelated antigen. The latter cells were also cloned and did not display this suppressive activity, were CD4+ and proliferated vigorously to M. leprae presented by autologous HLA-DR molecules. We shall refer to these cells as T helper (Th) cells. Most of the suppressive T cell clones (Ts) were also CD4+ and also proliferated to M. leprae presented by HLA-DR, but much less strongly than Th cells. In this study we report on our search for (a) the mechanism of this apparently antigen-specific suppression by T cells, and (b) a possible phenotypic difference between Th and Ts clones. The two main conclusions are that Ts clones possess a lytic machinery, but that M. leprae-specific suppression and cytotoxicity can be clearly dissociated, and that the only phenotypic difference between Th and Ts is the presence of the CD28 marker on Th and its absence on Ts clones.

A comparative study on the effects of rIL-4, rIL-2, rIFN-gamma, and rTNF-alpha on specific T-cell non-responsiveness to mycobacterial antigens in lepromatous leprosy patients in vitro

We have studied lepromatous leprosy (LL) as a human model disease for T-cell non-responsiveness to specific mycobacterial antigens and studied the effect of rIL-4, rIL-2, rIFN-gamma and rTNF-alpha thereon. T-cell non-responsiveness to Mycobacterium bovis bacillus Calmette-Guerin (BCG) or purified protein derivative of M. tuberculosis (PPD) antigens could be overcome in 5 out of 8 non-responder patients by rIL-2 and in 2 out of 8 by rIL-4. The ability of rIL-4 to overcome BCG/PPD non-responsiveness was strongly dose-dependent. When rIL-2 and rIL-4 were added simultaneously, they seemed to synergize in their effect. T-cell non-responsiveness to M. leprae could be overcome only in 2 out of 18 non-responders by rIL-2 but not by rIL-4 alone. The ability of rIL-2 to overcome T-cell non-responsiveness to M. leprae antigens became particularly marked when the recombinant 65-kDa heat shock antigen of M. leprae was used instead of whole bacilli. Exogenously added rIL-4, and to a lesser extent rIL-2, strongly enhanced existing T-cell responses to BCG or M. leprae in the majority (8 out of 11) of responders. These findings may have implications for the in vivo manipulation of the immune response by recombinant lymphokines and vaccines.

Induction of antigen-specific CD4+ HLA-DR-restricted cytotoxic T lymphocytes as well as nonspecific nonrestricted killer cells by the recombinant mycobacterial 65-kDa heat-shock protein

Acquired cell-mediated immunity to intracellular parasites like mycobacteria is dependent on antigen-specific T lymphocytes. We have recently found that mycobacteria not only induce helper T cells but also cytotoxic CD4+ and/or CD8+ T cells as well as nonspecific killer cells that lyse human macrophages in vitro. In addition, we have described that the recombinant heat-shock protein (hsp) 65 of Mycobacterium bovis BCG/M, tuberculosis is an important target antigen for CD4+CD8- cytotoxic T cells. We have now further investigated the cytotoxic effector cells that are induced by the hsp65 of BCG. Purified protein derivative of tuberculin (PPD)- or hsp65-specific cytotoxic T cells specifically lysed PPD, hsp65 of BCG and hsp65 of M. leprae-pulsed macrophages in an HLA-DR-restricted manner. Nonpulsed macrophages were lysed to a much lower but still significant extent. hsp65-induced effector cells expressed CD3, CD5, CD4, CD8 and CD56 markers. Depletion experiments showed that the antigen-specific HLA-DR-restricted killer cell was of the CD5+CD4+CD8-CD56- phenotype. Experiments using N-terminal truncated hsp65 fusion (cro-lacZ) proteins suggested that the N-terminal 65 amino acid residues of the 540 amino acid molecule are critical for the expression of the cytotoxic target epitope(s) in two individuals tested. In addition to inducing antigen-specific cytotoxic effector cells, the hsp65 also triggered nonspecific nonrestricted effector cells with lytic activity against nonpulsed autologous or allogeneic macrophages as well as K-562 and Daudi tumor cells. hsp65-stimulated effector cells produced both interferon and tumor necrosis factor-alpha. An important finding was that hsp65-stimulated effector cells strongly inhibited colony-forming unit formation from live BCG-infected autologous macrophages.

HLA-DR and -DQ antigens in malnutrition-related diabetes mellitus in Ethiopians: a clue to its etiology?

Thirty Ethiopian malnutrition-related diabetes mellitus (MRDM) patients were HLA typed and their HLA antigen frequencies were compared to those of 31 previously typed insulin-dependent diabetes mellitus (IDDM) patients and to 84 controls from the same ethnic background. In comparison to controls, a striking association between MRDM and HLA-DR3 (X2 = 15.15, p = 0.0001) was observed, whereas the frequency of HLA-DR4 was non-significantly increased (RR = 1.72). The frequency of DR2, DQw1, and DQw6 was decreased among MRDM. In comparison to IDDM that is associated with both DR3 and DR4 in this population, MRDM showed no significant differences in HLA class II antigens frequencies. Therefore, the genetic basis of susceptibility to MRDM and IDMM in Ethiopia is at least partially identical.

T cell responses to fractionated Mycobacterium leprae antigens in leprosy. The lepromatous nonresponder defect can be overcome in vitro by stimulation with fractionated M. leprae components

Protective immunity against Mycobacterium leprae is dependent on M. leprae-reactive T lymphocytes. M. lepare-directed T cell reactivity is high in the localized tuberculoid form of leprosy but specifically absent in the disseminated lepromatous type of the disease. Two important questions that are relevant for the understanding of the immune response in leprosy as well as for the design of rational immunoprophylaxis and -therapy strategies are: (a) what are the antigens that trigger T cell responses in tuberculoid patients and thus protect these individuals from developing lepromatous leprosy and (b) is it possible to restore T cell responsiveness to M. leprae in lepromatous patients by rechallenging the immune system with selected antigens that will trigger help but not suppression? We have addressed these question by directly probing the peripheral T cell repertoire of 10 tuberculoid and 18 lepromatous patients with large numbers of different M. leprae and BCG antigenic components that had been separated on the basis of their relative molecular mass (Mr) by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and electroblotted onto nitrocellulose. This technique allows the identification of T cell-stimulating antigens independent of the expression of B cell epitopes by these antigens. So far T cell epitopes have only been mapped on M. leprae proteins that had previously been defined by antibodies. Our results show that: (a) tuberculoid patients' T cells responded preferentially to M. leprae and BCG antigens in the lower (i.e. less than 70 kDa) Mr range with a peak in the 10-25 kDa range; (b) 6 out of 18 lepromatous patients that did not respond to whole M. leprae responded strongly to isolated M. leprae components; antigens in the lower Mr. range were recognized by five out of these six patients and thus commonly seen by both tuberculoid and lepromatous patients' T cells; however, antigens in the higher Mr range, in particular greater than 150 kDa, were only recognized by lepromatous patients' T lymphocytes; (c) furthermore, the T and B cell repertoires in leprosy patients are skewed towards different antigenic fractions.

The reconstitution of cell-mediated immunity in the cutaneous lesions of lepromatous leprosy by recombinant interleukin 2

Human rIL-2 (10-30 micrograms) was injected intradermally into the skin of patients with lepromatous leprosy with high bacillary loads. All patients responded to the lymphokine with local areas of induration that peaked at 24 h and persisted for 4-7 d irrespective of whether the site was "normal skin" or a nodular lesion. Within 24 h there was an extensive emigration of T cells and monocytes into the site. The percentage of the dermis infiltrated by mononuclear cells increased by more than sevenfold, peaking at 4 d and persisting for greater than 15 d. Both CD4+ and CD8+ T cells entered the site. T cells of CD4+ phenotype predominated at 2-7 d but by 11 d, CD8+ cells were predominant. Considerable numbers of T6+ Langerhans' cells appeared in the dermis by 72 h and persisted for 3 wk. By 4 d the thickness of the overlying epidermis had increased twofold, and keratinocytes were expressing MHC class II antigen and the IFN-gamma-induced peptide IP-10. Starting at 48 h, there was an extensive destruction of mononuclear phagocytes that contained structurally intact or fragmented M. leprae observed at the electron microscope level. The organisms, either free or contained within endocytic vacuoles, were discharged into the extracellular space and then reingested by blood-borne monocytes. This was followed by marked reductions in the number of acid-fast organisms in the injected site, evident as early as 4-7 d and more marked at 2-3 wk after injection. 13 of 15 patients exhibited a disposal of acid-fast bacilli ranging from 5- to 1,000-fold with a mean value of approximately 100-fold. The administration of IL-2 leads to the generation of an effective cell-mediated immune response, recapitulating an antigen-driven event and leading to striking local reductions in M. leprae. In comparison with the purified protein derivative of tuberculin reaction, bacilli are cleared more promptly, although emigratory cells persist for a shorter time.

The recombinant 65-kD heat shock protein of Mycobacterium bovis Bacillus Calmette-Guerin/M. tuberculosis is a target molecule for CD4+ cytotoxic T lymphocytes that lyse human monocytes

Since little is known about Tc cells in the human immune response to intracellular parasites, we have studied the role of Tc cells in response to M. bovis Bacillus Calmette-Guerin (BCG). Donors whose PBMC responded to BCG, purified protein derivative (PPD), and the recombinant 65-kD heat shock protein (HSP) of BCG generated BCG/PPD-specific CD4+ effector T lymphocytes that lysed PPD as well as recombinant 65-kD-pulsed monocytes. Nonpulsed or irrelevant antigen-pulsed target cells were lysed to a much lower but still significant extent. PPD-stimulated effector lymphocytes of a recombinant 65-kD nonresponder lysed PPD but not recombinant 65-kD-pulsed monocytes. Recombinant 65-kD-educated effector lymphocytes lysed both recombinant 65-kD- and PPD-pulsed monocytes. In addition, these effector cells efficiently lysed nonpulsed target cells. These results demonstrate that in recombinant 65-kD responders, the recombinant 65-kD HSP of BCG is an immunodominant target as well as a triggering molecule for BCG/PPD-specific CD4+ cytotoxic T cells that lyse autologous monocytes. The implications of these findings with respect to the role of the 65-kD HSP in autoimmunity are discussed.