Antibody reactions to virus specific early antigens (EA) in patients with cytomegalovirus (CMV) infection

A cytomegalovirus (CMV) induced early antigen (EA) was demonstrated in fibroblasts infected in the presence of the DNA inhibitor cytosine arabinoside (Ara C). In the dose used (20 μg/ml) Ara C blocked DNA synthesis completely, as judged by thymidine incorporation and autoradiography. The percentage of EA positive cells was 0.6 8 hr post infection, increasing to 50 and 65% on the 2 following days. EA differed from late antigens (LA), present in CMV infected but otherwise untreated fibroblasts, with regard to distribution and antigenic specificity. Sera differed in their reactivity to EA at comparably high anti LA titres. Direct immunofluorescence staining of EA positive cells was only blocked with high titred anti EA sera, but not with high titred anti LA sera with a low or negative anti EA titre. Anti CMV EA did not cross react with antibodies against EBV, Herpes simplex or varicella/zoster. A collection of 115 serial sera from 45 acutely CMV infected patients was tested for anti EA and anti LA antibodies. The diagnosis was confirmed by the occurrence of a significant rise in CF antibodies and/or virus isolation.