Antibody classes and subclasses in circulating immune complexes isolated from mice infected with lactic dehydrogenase virus.

A chronological study of circulating immune complexes (CIC) in lactic dehydrogenase virus (LDV)-infected mice has been performed. The results demonstrate that CIC containing immunoglobulin of the IgM class were isolated between days 3 and 9 post-LDV infection and corresponded to an increase in serum IgM. IgG1-containing CIC were also transient in the serum of LDV-infected mice in that they were isolated only between days 5 and 13. The occurrence of IgG1 CIC did correlate with an increase in total IgG1 in the serum, however, it did correlate with a small (1:10) increase in IgG1 anti-LDV activity. In contrast, CIC containing immunoglobulin of the serum IgG2 subclass were not isolated from LDV-infected serum until 15 days post infection. This chronological appearance of IgG2 CIC did not correlate with the observed increase in total IgG2 concentration in LDV-infected mice on day 7, however, was analogous to the rapid increase in free serum LDV-specific antibody. We propose that the non-specific suppression of the immune response and tumour enhancement during the acute phase of LDV infection could be due to the immunoregulatory properties of IgG1 CIC.