Differentiation of recent and past infections with Legionella pneumophila by determination of specific IgM.

The ELA-IgM antibody test as used in viral diseases can also be applied to infections with Legionella pneumophila and is yielding similar results as the IgM determination by immunofluorescence. Complement-fixation and microagglutination are yielding also positive results in IgM-positive sera. IgM antibodies appear relative late after beginning of the disease and are persisting for several months. There is evidence that IgM antibodies as detected by the use of a Legionella pneumophila antigen are also cross-reacting to a number of other antigens.

A "reverse" solid-phase radio-immuno-assay for IgM-antibodies to hepatitis A virus.

A "reverse"solid-phase radio-immuno-assay for IgM antibodies to hepatitis A virus (HAV) was developed. Anti-human IgM immunoglobulins were bound on the wells of polyvinylchloride microtiter plates. Serum specimens were incubated in the anti-human IgM coated wells and bound IgM antibodies were then assayed for antigen specificity by subsequent incubations with HAV antigen and 125I-labelled human anti-HAV IgG. The test showed a high sensitivity and specificity for anti-HAV IgM antibodies. No false-positive reactions were observed either in the sera from patients with hepatobiliary disorders other than HAV infection or in the sera containing both rheumatoid factor and anti-HAV IgG antibodies. In acute HAV infections specific IgM antibodies were present already in the first specimens taken within a few days after the onset of jaundice. The persistence of the IgM antibodies was from 4 to 6 months. IgM antibody titers up to 1,000,000 were observed in the acute phase of HAV infection. In routine diagnostic work the titration of the sea was not necessary, since a reliable qualitative result was obtained by testing the sera in a single dilution of 1:100. A similar "reverse" immuno-assay principle may be adaptable for the diagnostic determination of IgM antibodies to different viral and microbial antigens.

Solid-phase enzyme immunoassay for determination of antibodies to cytomegalovirus.

A solid-phase enzyme immunoassay for the determination of immunoglobulin H (IgG) and IgM antibodies to cytomegalovirus is described. The enzyme immunoassay gave reliable and consistent results which were in concordance with those obtained by the complement fixation test and the indirect immunofluorescence test. Antibodies to herpes simplex and varicella-zoster viruses did not interfere in the enzyme immunoassay for cytomegalovirus IgM antibodies. In a few patients with IgM antibodies to Epstein-Barr virus, cytomegalovirus IgM antibodies were also detected. False-positive cytomegalovirus IgM antibody results were observed in sera containing both the rheumatoid factor and cytomegalovirus IgG antibodies. This rheumatoid factor interference was overcome by the absorption of sera with polymerized human gamma globulin. The absorption did not affect true cytomegalovirus IgM antibody titers. Also described is a simple enzyme immunoassay that makes possible a more sensitive detection of the rheumatoid factor than the latex agglutination test.