In situ detection of DNA and mRNA of human cytomegalovirus to distinguish different forms of viral infection in leukocytes

In situ PCR and in situ reverse transcription PCR (RT-PCR) were applied to discriminate between latent and productive infection of human cytomegalovirus (HCMV) in leukocytes. We investigated 28 samples, in which viral pp65 antigen was detected only in the cytoplasm of leukocytes. Additionally we assayed 12 specimens lacking pp65 antigen. Using nested PCR (nPCR), viral DNA was detected in 27 samples. In six samples the results of nPCR were unreadable due to the presence of polymerase inhibitors. By application of in situ PCR, we were able to confirm the presence of viral DNA in the nucleus and/or cytoplasm. Productive infection was recognized in 20 samples in which transcripts for late viral genes were detected. Among the 20 samples negative by in situ RT-PCR, we recognized phagocytosis of viral particles in eight and the latent form of HCMV infection in five.