Detection of IgM and IgA HIV antibodies after removal of IgG with recombinant protein G.

Indirect assays for IgM and IgA antibodies often lack sensitivity and specificity due to interference from IgG antibodies. To overcome this problem we have developed a simple procedure using recombinant protein G coupled to agarose beads to remove the interfering IgG. A series of HIV seroconversion panels was tested by IgM and IgA immunoblot after protein G treatment in order to evaluate IgG removal and to study appearance of IgM and IgA antibodies in early HIV infection. Protein G treatment removed 99.9% of the IgG and reduced IgG anti-HIV titers of over 1/100,000 to undetectable levels. Both IgM and IgA HIV antibodies were detected as early in seroconversion as were IgG HIV antibodies. IgA HIV antibodies persisted for a longer period of time, reacted with more HIV proteins, and showed more intense staining than IgM HIV antibodies.