The detection of the epstein‐barr virus (ebv) nuclear antigen (ebna) by anti‐complement immunofluorescence. Immunoglobulin class of antibodies and role of complement

The Epstein-Barr virus (EBV)-associated nuclear antigen (EBNA) was detected by anti-complement immunofluorescence (ACIF) in Raji lymphoblastoid cell line, and the mechanism of the reaction explored, using Ig fractions of anti-EBNA sera and purified components of complement. Following fractionation of serum from 13 donors, anti-EBNA antibodies were always found to be associated with IgG, but were also detectable in the IgM fraction of four sera. Sequential addition of functionally pure complement components in the ACIF reaction showed that the classical sequence of complement activation is involved. Anti-EBNA antibody reactions in Raji cell nuclei can also be detected by anti-Ig immunofluorescence with a low level of sensitivity. The same pattern of granular fluorescence was observed when C3 (β1A/β1C), or C4 or IgG anti-EBNA antibodies were revealed with the corresponding fluorescein-conjugated reagents. Blocking of the ACIF reaction was achieved with Fab'2 anti-EBNA antibody fragments, which therefore provided an appropriate specificity control for the detection of EBNA.