Anti M-protein antibody response to type A or B natural influenza detected by solid phase enzyme linked immunosorbent assay and by complement fixation.

Anti M-protein antibody response has been looked for in sera from individuals with serological evidence of A or B influenza infection using pure M-protein (M) in complement fixation tests (CF), in IgG and in IgA specific enzyme linked immunosorbent assays (ELISA). Mp ELISA (IgG specific) antibodies are not restricted to people with history of recent respiratory infection. Individuals under 15 years are less prone than those older to display M ELISA activity. Most M ELISA positive individuals are also nucleoprotein (NP) positive. There are more M than NP ELISA positives in the influenza A series whereas the reverse is observed in the influenza B series. Most of the M ELISA positives are also S CF (standard soluble antigen CF) positive indicating that M ELISA IgGs are related to recent infections. Some sera exhibit M ELISA activity with no other evidence of influenza experience than V CF (viral antigen CF) or HI (haemagglutination inhibition), suggesting that some recent influenza infections are better traced with M ELISA than with S CF. Amongst chronic bronchitis patients with V CF or HI antibodies to A2 influenza virus but no type A S CF activity, the proportion of M ELISA positives averages 40 per cent. This fact as well as two other features of that group i.e. cases with long lasting S CF activity and occasional virus isolation several months after the initial acute infection, suggest that influenza virus might cause prolonged infection in some patients with chronic bronchitis.