1Youssef Khodery, ¹Mohamed Youssef Khalil and ²Hamdy M Mostafa.

Departments of ¹Microbiology and Immunology, and ²Tropical medicine, Faculty of Medicine, Al-Azhar University, Assuit, Egypt.

In spite of the overwhelming susceptibility to leishmaniasis, BALB/c mice can give Th1 response to multiple epitopes of the major promstigote surface protease (PSP or gp63). Here we investigated the cellular basis of immune response to the overlapping peptides of the most powerful epitope. It was found that when the response was examined by recall with overlapping peptides, the central peptide (364-378) preferentially induces Th1 response while the boundary peptides (361-375, & 368-382) preferentially stimulate Th2 response. A critical issue in designing a peptide vaccine is to demonstrate that it leads to a powerful Th1 protective immune response on recall with the native antigen. So it was found that a strong Th1 response was produced when the central peptide (364-378) was used in priming and the native gp63 was used for recall. The opposite was true when the boundary peptide was used in priming and the native gp63 was used for recall. The use of anti-IFN-g antibody revealed that the central peptide (364-378) could induce Th2 response, and the use of anti-IL-10 revealed that the periphery peptides could induce Th1 response, indicating that the Th1 or Th2 responses would develop under favorable conditions which may be a complex pattern of reciprocal lymphokine regulation.