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Role of microvariation in T cell epitopes in weak B cell immunogenicity of protective PorA antigens

Thursday 17 January 2013

dr Cecile van Els

Research at the new center for Immunology of Infectious Diseases and Vaccines (cIIV) (at RIVM) is focused at mapping the mechanisms of protective immunity against various pathogens. Immunity to serogroup B meningococci, a major cause of meningitis (‘nekkramp’), is predominantly mediated by bactericidal antibodies against ‘loop 4’ of PorA, the variable outer membrane protein. Interestingly, the most abundant circulating PorA subtype, P1.7-2,4 (P1.4), appears to be the least immunogenic, evoking low bactericidal antibody titers. Another serosubtype P1.5-1,2-2 (P1.2) is regarded as a prototype of a strong immunogenic PorA, evoking high bactericidal antibody responses. We identified a shared human and murine CD4+ T helper cell epitope in PorA, upstream of the ‘loop 4’ B cell epitope, that shows microvariation at two amino acid residues. The P1.2 allele of this epitope (Glu171; Ala184) is recognized by human and mouse T cells, whereas the P1.4 allele is not (Asp171; Ile184). We hypothesize that the quality of anti-loop 4 antibody responses depends on the presence of T cell reactivity against this particular T cell epitope, through so-called ‘deterministic linkage of B and T cell epitopes’ (ref 2). Recently we engineered a set of PorA mutants, exchanging amino acid residues at positions 171 and 184 between the P1.2 and P1.4 serosubtypes. The goal of this student project is to study the role of position 171 and 184 microvariation in the induction and functional maturation of antibody responses against PorA. Mutant PorA antigens will be tested in vitro for recognition by monoclonal antibodies and human T cell clones to verify their combination of ‘loop 4’ specificity and allelic T cell epitope variant. Then, sera and splenic cell suspensions from mutant PorA immunized mice will be analysed for patterns of functional B and T cell responses, to determine the role of Glu171-Ala184 residues in the immunogenicity of meningococcal PorA.

Isolation and culturing of murine and human cells (lymphocyte isolation, T-cell clones, cell lines, transfections), Biochemistry (SDS-PAGE, western blot), Immunology (B-ELISPOT, ELISA, FACs analysis, specific T cell proliferation and multipex cytokine assays)

6 or 9 months

Dr C.A.C.M. van Els, cecile.van.els@rivm.nl