Immunologic mechanisms of the tube leukocyte adherence inhibition assay in adjuvant-induced disease in rats.

In the leukocyte adherence inhibition assay (LAI), splenic leukocytes from normal and adjuvant-induced disease (AID) rats were incubated with synovial extracts obtained from AID and normal joints. The proportion of leukocytes nonadherent to the surface of a glass tube in the presence of either AID or normal synovial extract was compared and this difference was expressed as a nonadherent index (NAI). The AID rats have significantly higher NAI scores (29 +r4) than normal rats (0 +r5). Preincubation of splenic leukocytes from normal rats with sera from AID animals caused these normal cells to respond with positive NAI scores (25 +r6). The IgG fraction from AID sera was shown to be an important component in arming these normal splenic leukocytes and a dose response curve was noted. Preincubation of AID splenic leukocytes with antiserum to rat IgG abrogated the positive NAI scores, whereas antiserum to rat IgM had no effect on the NAI values. The reactive cell in the LAI assay was a mononuclear cell whose activity was removed by adherence to plastic petri dishes. We suggest that IgG plays an important role in the LAI assay and might bind to plastic adherent mononuclear cells (monocytes?), through their Fc receptor to allow these cells to react with AID synovial extracts.