Crossreactions and sequence homologies between recombinant polypeptides from Leishmania aethiopica and human IgG and IgM.

Recombinant DNA fragments M (154 bp) and G (206 bp), coding for recombinant polypeptides that crossreact with human IgM and IgG, have been isolated from a genomic library of Leishmania aethiopica. Epitope scanning of the two recombinant polypeptides, using overlapping octapeptides, revealed several crossreactive epitopes present in both recombinant proteins. By comparing amino acid sequences, similar sequences in human mu and gamma immunoglobulin heavy chains were identified. One of the parasite octapeptides is identical to an octapeptide in gamma1 covering the Gm(a) allotypic marker. Expression of both the M and G fragments was detected in the parasites by RT-PCR of total mRNA, using primers specific for these fragments. Preliminary data showed that the presence of autoimmune anti-IgG antibodies was more pronounced in sera from patients with diffuse cutaneous leishmaniasis than in sera from patients with localised cutaneous leishmaniasis. We suggest that these immunoglobulin-crossreacting epitopes potentially might contribute to the induction of rheumatoid factors and be involved in the interplay between the parasite and the host immune system.