Heat shock proteins as antigens of bacterial and parasitic pathogens.

There is general agreement that a function, perhaps the major function, of stress proteins under normal physiological conditions is to help assembly and disassembly of protein complexes and to catalyse protein-translocation processes. It remains unclear, however, as to what role these processes play in stressed cells. It could be that cells under stress produce abnormal, misfolded or otherwise damaged proteins and that increased synthesis of stress proteins is required to counter protein modifications. A role for stress proteins in recovery of cells from stress, as opposed to a role in helping cells to withstand a lethal stress, is thus suggested. The intracellular location of stress proteins, in the unstressed and stressed cell, is worthy of further studies. Members of the hsp70 family are associated with the cytosol, mitochondria and endoplasmic reticulum. There is evidence, particularly from studies on mammalian cells (Tanguay, 1985; Welch and Mizzen, 1988; Arrigo et al., 1988), that following stress hsps migrate to various cellular compartments and subsequently delocalize after stress. However, there is little comparable data from microbial systems for this phenomenon (e.g. Rossi and Lindquist, 1989). The question as to the role of stress proteins in the transient acquisition of thermotolerance remains to be answered. It is insufficient to equate the kinetics of stress-protein synthesis with acquisition of thermotolerance. Quantitative data on the amount of stress protein present at various times, including the recovery period, is required. The demonstration that microbial stress proteins are important antigenic determinants of micro-organisms causing major debilitating diseases in the world is an exciting observation. Studies on the interplay of pathogen and host, both carrying similar antigenic hsp determinants, will be a challenging area for future research. It is likely that E. coli and Sacch. cerevisiae, with their well-established biochemical and genetic properties, will continue to be the experimental systems of choice for studies on stress proteins. On the other hand, it is encouraging that studies on other micro-organisms have expanded in the past few years and have made substantial contributions towards our understanding of the stress response. The ubiquitous nature of the stress response and the remarkable evolutionary conservation of the stress proteins continue to be attractive areas for research.

Microbial stress proteins

A 17-kDa lipoprotein, TUL4, of the facultative intracellular bacterium Francisella tularensis is one of several membrane proteins that induce an in vitro response in T cells from F. tularensis-primed humans. A DNA fragment of the live vaccine strain F. tularensis LVS encoding TUL4 was cloned into Salmonella typhimurium chi 4072, an attenuated delta cya delta crp mutant. Expression of the protein by the recombinant S. typhimurium chi 4072 (pTUL4-15) was maintained after passage in BALB/cJ mice. When mice were immunized with S. typhimurium chi 4072(pTUL4-15), some animals showed an antibody response and a T-cell response to TUL4. When the immunized mice were challenged with the live vaccine strain F. tularensis LVS, bacterial counts in the liver and spleen were lower than in animals immunized with S. typhimurium chi 4072. Immunization with F. tularensis LVS caused a much stronger protection against the challenge than did immunization with S. typhimurium chi 4072(pTUL4-15). The present study demonstrated that the 17-kDa lipoprotein TUL4 of F. tularensis is involved in a protective immunity to tularemia. Possibly, several T-cell-reactive proteins of the organism have to contribute for optimal protection to be achieved. Images

https://iai.asm.org/content/iai/60/7/2855.full.pdf

Humoral and cell-mediated immunity in mice to a 17-kilodalton lipoprotein of Francisella tularensis expressed by Salmonella typhimurium.

Most of the antigens of Mycobacterium leprae and M. tuberculosis that have been identified are members of stress protein families, which are highly conserved throughout many diverse species. Of the M. leprae and M. tuberculosis antigens identified by monoclonal antibodies, all except the 18-kDa M. leprae antigen and the 19-kDa M. tuberculosis antigen are strongly cross-reaction between these two species and are coded within very similar genes. Studies of T cell reactivity against mycobacterial antigens have indicated that M. tuberculosis bears epitopes that are cross-reactive with the M. leprae 18-kDa antigen, but attempts to identify an 18-kDa antigen-like protein or protein coding sequence in M. tuberculosis have been unsuccessful. We have used a combination of low-stringency DNA hybridization and polymerase chain reaction techniques to identify, isolate, and sequence genes from M. avium and M. intracellulare that are very similar to the 18-kDa antigen gene of M. leprae and others that are homologs of the 19-kDa antigen gene of M. tuberculosis. Unlike M. leprae, which contains a single 18-kDa antigen gene, M. avium and M. intracellulare each have two 18-kDa antigen coding sequences. Although the M. leprae, M. avium, and M. intracellulare 18-kDa antigen genes are all very similar to one another, as are the M. tuberculosis, M. avium, and M. intracellulare 19-kDa antigen genes, we have been unable to detect any 18-kDa antigen-like coding sequences in DNA from M. tuberculosis.

Homologs of Mycobacterium leprae 18-kilodalton and Mycobacterium tuberculosis 19-kilodalton antigens in other mycobacteria.

Human CD8 T lymphocyte clones (TLC) were generated from the pleural effusion of patients with tuberculosis using a protocol that required, in addition to antigen, coculture of purified CD8+ T cells, accessory cells, interleukin 2 (IL2) and anti-CD3-Sepharose. The TLC obtained were stimulated by mycobacterial soluble extracts in an IL2-dependent and MHC class I-restricted manner. When antigen-responsive TLC were screened with extracts from the recombinant mycobacterial library they were found to respond to either the Y3125 (100-kDa) or the Y3111 (71-kDa) lambda gt11 clones. Polyacrylamide gel immunoblot analysis demonstrated that the CD8 TLC responded to fractions with the molecular mass range 27-45 kDa in the Y3125 lysogen and 60-90 kDa in the mycobacterial soluble extract. The specificity of TLC reactive with the Y3111 clone was confirmed using the 71-kDa antigen purified from the same lysogen. These TLC recognized sequences common to the 71-kDa protein derived from mycobacteria, E. coli or a human cell line. Studies of three TLC using antigen-presenting cells of known genetic haplotype indicated that stimulation with both the Y3125 and the 71-kDa antigens were restricted by determinants encoded by HLA-B8.

Specificity of proliferative response of human CD8 clones to mycobacterial antigens.

Mycobacterial antigens which play a major role in humoral and cell-mediated immune recognition are related to proteins which are induced in response to stress stimuli. The potential involvement of stress-induced proteins in infectious disease and in autoimmune responses is discussed.

Stress-induced proteins and the immune response to leprosy.

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Stress-induced proteins and the immune response to leprosy.