Elimination of nonspecific cytomegalovirus immunoglobulin M activities in the enzyme-linked immunosorbent assay by using anti-human immunoglobulin G.

Direct enzyme-linked immunosorbent assay methods offer several advantages in assessing past or recent exposure to cytomegalovirus (CMV) infection, but there persist many pitfalls in the use of these methods for determining specific immunoglobulin M (IgM). The efficiency of absorption of sera by IgG-coated latex beads, aggregated human IgG, or Staphylococcus aureus, i.e., for removing nonspecific CMV IgM activities, was evaluated in comparison with the effect of an anti-human IgG hyperimmune serum. Large routine series comprising serum samples from patients of various clinical groups and healthy individuals were examined. The CMV IgM-positive samples were at first treated with latex or aggregated IgG, but these absorptions left too many CMV IgM-positive individuals. S. aureus increased the nonspecific activity of some sera and, in other cases, removed or impaired specific IgM activities. The anti-IgG treatment caused the disappearance of nonspecific CMV IgM activities that had resisted the other treatments, whereas specific activities remained intact. Utilizing this method, only 1.03% of the routine series patients remained CMV IgM positive by the enzyme-linked immunosorbent assay, a figure in good agreement with a mean probability of CMV antibody acquisition of 0.33% for the population living in Belgium. On the other hand, in a series of patients who were investigated for serological response to several viruses, eight individuals displayed multiple IgM activities after anti-IgG treatment. In these cases, most IgM activities were found in patients who had IgG toward the related antigen for a long time before transient IgM was detected. This result implies that to assess a diagnosis of primary infection, it is necessary to examine serial specimens for IgG acquisition accompanying specific IgM.