Cytomegalovirus-directed lymphocyte reactivity in healthy adults tested by a CMV-induced lymphocyte transformation test.

A cytomegalovirus (CMV) induced lymphocyte tranformation test (LTT) performed as a microtechnique assay is described. Investigations were done in a group of twenty-five healthy adults with normal lymphocyte reactivity to phytohaemagglutinin and previously encountered antigens. Lymphocyte reactivity was established in CMV-seropositive persons using heat-inactivated cell-free CMV strain AD 169 in an optimal stimulating dose of 10(1-5) TCID 50. Positive CMV-LTT results were shown to be induced by purified inactivated CMV. Most persons (twelve out of seventeen) with antibodies against CMV-induced late or virus-structure antigens (LA) showed positive (stimulation index greater than 2-0) CMV-LTT results. Magnitude of CMV-LTT responses was positively related to the CMV-LA Ab titres (P less than 0-01). All persons (six) with antibodies against CMV early or non-structural antigens showed positive CMV-LTT results and highest stimulation rates were found in this group. Generally CMV-seronegative persons were non-responsive. Only in one case (LA Ab titre 10) a borderline positive response (stimulation index 2-3) was seen. The CMV-LTT was shown to have virus-specific properties because it was not related to simultaneously performed LTTs with Epstein-Barr virus and Herpes simplex virus in the same persons. It is concluded that CMV-LTTs are useful virus-specific in vitro techniques for the study of CMV-directed lymphocyte reactivity. Its possible relationship to other cell-mediated immunity tests and its practical applications are discussed.