Background: Infections with human herpes virus 6 (HHV-6) are very common. After primary infection, the virus remains latent and persists at low level in cells and tissues. Not usually associated with disease in the immunocompetent host, HHV-6 infection is a major cause of opportunistic viral infections in the immunosuppressed. The different stages of HHV-6 infection are difficult to characterize in the laboratory.
Objectives: The aim of this paper was to assess the isotype patterns of IgG antibodies against HHV-6 in seropositive subjects during different stages of the virus activity.
Study design: From a total of 190 human serum samples from 43 healthy children, 24 pregnant women and 24 patients with bone marrow transplants, 111 sera were processed by indirect immunofluorescence assay for the detection of IgG1, IgG2, IgG3 and IgG4 specific antibodies. The mean geometrical title (MGT) of the antibodies was calculated.
Results: All pregnant women had IgG1 (24/24; 100%; MGT 46). A 95% (41/43) of healthy infants had IgG1 (MGT 57). In bone marrow transplants, 58% (14/24) of the patients showed seroconversion (MGT 529) with an isotype response of IgG1 and IgG4 during the observation period. Remaining bone marrow transplant patients, who had the IgG without any variations (MGT 184), had isotype IgG1.
Conclusions: These results revealed two different immune isotype response patterns. One of them is restrictive to IgG1 in the latent phase of HHV-6 infection in healthy children, pregnant women and transplant patients with stable levels of antibodies whereas IgG1 and IgG4 are detected in the reactivation of HHV-6 in transplant patients. The IgG isotype immune responses may contribute to the existing set of serological markers in characterizing the different stages of natural infection of HHV-6.