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A new test principle for the detection of specific IgM-class antibodies was developed and applied in an Enzyme-Linked Immuno Sorbent Assay (ELISA) for the detection of hepatitis A IgM antibodies. A solid phase coated with anti-IgM was incubated successively with serum sample, specific antigen, and enzyme-labeled F (ab')2 fragments from IgG antibodies against the antigen and enzyme substrate. F(ab')2 fragments were used to avoid interference with rheumatoid factor. Specificity and sensitivity are very high. This test principle appears generally applicable in the diagnosis of infectious and parasitic diseases by testing only one serum sample.

Purified lymphocytes from human tonsil and adenoid specimens were cultured with and without phytohemagglutinin. Adenovirus was isolated from lymphocytes of 8 of 90 specimens tested. With one exception, it was necessary to culture the lymphocytes before infectious virus could be detected. Phytohemagglutinin stimulation enhanced the recovery of virus. The results suggest that lymphocytes in tonsils and adenoids may be naturally infected with adenovirus and that, in positive cultures, at least 1 of every 107 cells harbors virus or viral precursor at initiation of the cultures. Adenovirus was demonstrated directly in fresh suspensions of unpurified cells from tonsils and adenoids in seven cases. In five of these cases, at least 1 of every 106 cells contained infectious virus. Adenovirus was isolated from 61 (62%) of 98 tonsil and adenoid specimens by the conventional method of tissue fragment culture after various periods of cultivation. The viruses isolated were of serotypes 1, 2, 5, and 6.

A direct enzyme-linked immunosorbent assay was developed for the measurement of immunoglobulin M (IgM) antibody to cytomegalovirus (CMV). Wells of microtiter plates were coated with anti-human IgM. Each patient's serum was added at a dilution of 1:100, and IgM from the serum was allowed to react with anti-human IgM. The amount of CMV-specific IgM antibody bound was determined by measuring the intensity of color change after the addition of peroxidaselabeled CMV antigen and substrate. Nuclei of infected cells served as an antigen source. CMV IgM could be detected only in IgM fractions of sera from patients with a recent CMV infection. Rheumatoid factor did not cause false-positive results. No cross-reactions were observed when paired sera from 22 patients with herpes simplex or varicella and single sera from 12 patients with suspected infectious mononucleosis were tested by the direct enzyme-linked immunosorbent assay. Each of 17 patients with a seroconversion for CMV antibody showed CMVspecific IgM antibody. In six of these patients the antibody was detected in the initial serum. The direct enzyme-linked immunosorbent assay for CMV IgM is a specific and sensitive test for the diagnosis of recent CMV infections and possesses distinct advantages over indirect tests. 18 to 72 years of age. Four patients were children 3, 4, 9, and 15 years of age, none of whom had been congenitally infected with CMV. In addition, sera were obtained from 34 patients clinically suspected of having herpes simplex or varicella-zoster infection or infectious mononucleosis. Furthermore, 36 sera with 416

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