Enhanced uptake by guinea-pig macrophages of radio-iodinated human aggregated immunoglobulin G in the presence of sera from rheumatoid patients with cutaneous vasculitis.

A competitive radiobioassay method for soluble immune complexes in sera has been used to study sera from patients with rheumatoid arthritis. Twenty-eight out of sixty-two sera from selected seropositive rheumatoid patients were found to produce enhanced uptake of radio-iodinated human aggregated IgG by guinea-pig macrophages in contrast with the inhibition of uptake seen with SLE sera. Twenty-two out of the twenty-eight enhancing sera belonged to patients with cutaneous vasculitis. None of the twenty-two sera from seronegative rheumatoid patients possessed enhancing properties and none of these patients had clinical evidence of vasculitis. Three patients with seropositive SLE had sera with enhancing properties and had cutaneous vasculitis. We have shown that the enhancement is probably due to the presence in sera of immune complexes or altered IgG bound to rheumatoid factor. The possible mechanism has been investigated and it appears that there is increased binding of radio-iodinated aggregated IgG to free valencies on rheumatoid factor already bound to immune complexes.