Auto-transporter A protein of Neisseria meningitidis: a patent CD4(+) T-cell and B-cell stimulating antigen detected by expression cloning

A meningococcal genomic expression library was screened for potent CD4+ T-c ell antigens, using patients' peripheral blood lymphocytes (PBLs). One of t he most promising positive clones was fully characterized, The recombinant meningococcal DNA contained a single, incomplete, open reading frame (ORF), which was fully reconstructed with reference to available genomic sequence data. The gene was designated autA (auto-transporter A) as its peptide seq uence shares molecular characteristics of the auto-transporter family of pr oteins. Only a single copy of this gene was detected in the meningococcal, and none in the gonococcal, genomic sequence databases. The complete autA g ene, when cloned into an expression vector, expressed a protein of approxim ately 68 kDa, Purified rAutA recalled strong secondary T-cell responses in PBLs of patients and some healthy donors, and induced strong primary T-cell responses in healthy donors. The human B-cell immunogenicity and cross-rea ctivity of AutA, purified under native conditions, was confirmed in dot imm unoblot experiments. Immunoblots with rabbit polyclonal antibodies to rAutA demonstrated the conserved nature, antigenicity and cross-reactivity of Au tA amongst meningococci of different serogroups and strains representing di fferent hypervirulent lineages. AutA showed homology with another meningoco ccal and gonococcal ORF (designated AutB), AutB was cloned and expressed an d used to raise an autB-specific antiserum. Immunoblot experiments indicate d that AutB is not expressed in meningococci and does not cross-react with AutA, Thus, AutA, being a potent CD4(+) T-cell and B-cell-stimulating antig en, which is highly conserved, deserves further investigation as a potentia l vaccine candidate.