Human T-cell response to meningococcal immunoglobulin A1 protease associated alpha-proteins
Jose, J.; Wölk, U.; Lorenzen, D.; Wenschuh, H.; Meyer, T.F.
Scandinavian Journal of Immunology 51(2): 176-185
2000
ISSN/ISBN: 0300-9475 PMID: 10722372 Document Number: 525840
A unique feature of the immunoglobulin A1 (IgA1) protease from pathogenic Neisseriae, i.e. N. meningitidis and N. gonorrhoeae, is its co-secretion with an amphipathic alpha-protein. Polymerase chain reaction (PCR) analysis of the respective igaalpha gene region in 48 meningococcal strains revealed that this protein domain is conserved throughout all isolates in four different principal variants. Despite strain-dependent size and sequence variations, sequence analysis showed common structural characteristics. More than 80% of the amino acid sequence of all alpha-proteins is dependent on the five amino acids Q, E, A, K and R, resulting in a pI>10. The sequences are highly conserved at the N-terminus and the C-terminus and contain long amphipathic alpha-helical stretches. These stretches have a strong probability of forming coiled coil conformations and comprise short repetitive sequence modules with pronounced similarities to T-cell epitopes. We therefore analyzed the T-cell response of 20 volunteer blood donors to four peptides, representing such predicted epitopes, and a recombinant meningococcal alpha-protein. Sixteen donors reacted against at least one peptide after culture of peripheral blood mononuclear cells in interleukin (IL)-2-rich medium, while two individuals showed a positive reaction only against an IgA1 protease-derived control peptide. From one donor, we established and maintained T-cell clones specific for purified alpha-protein. Characterization of the T-cell clones revealed a CD3- and a CD4-positive phenotype and the secretion of IL-2 and interferon-gamma (IFN-gamma), but not of IL-4. This indicates an important role of alpha-proteins during meningococcal carriage and neisserial infection.