J. E. R. Thole

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

By screening a Mycobacterium lepraeλgt11 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 265–327 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.

Immune Reactions Against Heat Shock Proteins and Arthritis

During the last decade our insight into the aetiology and pathogenesis of supposedly autoimmune diseases like rheumatoid arthritis made considerable progress: they seem to be helper T lymphocyte (T cell) mediated; possible triggering and/or target antigens have been identified and aberrant expression of human leucocyte antigens (products of the HLA system, the human major histocompatibility complex) may be involved in the presentation of these antigens to helper T cells. The helper T cell, which is a class II-restricted CD4 positive T cell, plays a central role in orchestrating the immune response. The way it does so is by producing cytokines or lymphokines, which regulate, at least, all the other activated (by antigen) players of the immune system. Thus the most specific and efficient immunotherapy for an autoimmune disease is to shut off the button that specifically turns on the autoreactive helper T cell. That button is the HLA molecule presenting an autoantigen to the T cell receptor of an autoreactive helper T cell. How this button for autoreactive helper T cells (Th) may indeed be turned off very efficiently, has been shown in experimental animal models and has been further discussed in the previous chapter by Kingsley and Panayi on Immunotherapy. One such animal model that has stimulated a lot of research in this direction has been adjuvant arthritis (AA), which is induced in susceptible animals (Lewis rats) by the injection of Mycobacterium tuberculosis in oil. In this model, helper T cells from affected Lewis rats have been isolated that are capable of transferring the disease to naive animals. These T cells recognize epitopes on a mycobacterial heat shock protein of 65 kDa (hsp65). In this chapter we will review the studies performed in the last 6 or 7 years, that have addressed the possible role of heat shock proteins, and in particular hsp65, in the pathogenesis of, respectively, reactive and rheumatoid arthritis.