The sera of eleven persons with cutaneous vasculitis following streptococcal infection had less antibody than the sera of sixteen persons convalescent from similar infection without vasculitis, to M protein from the culture isolated from the serum donor and tested by monospecific antiglobulin haemagglutination, and to group A polysaccharide tested by latex particle agglutination.
The sera were assayed for neutralizing antibodies to streptolysin O, streptokinase, hyaluronidase, proteinase and erythrogenic toxin. The mean titres of each antitoxin for the groups of persons with or without vasculitis after streptococcal infection were similar, and were higher than the mean titres for ten normal, uninfected persons. The two groups of infected persons differed, in that persons without vasculitis formed antibody to each toxin synthesized by the cultures isolated from the serum donor, whereas persons with vasculitis formed little or no antibody to one or two of the toxins synthesized by the cultures isolated from them, though responding well to the other toxins.
If cutaneous vasculitis is induced by complexes of bacterial antigen with antibody, low levels of antibody could predispose the person to formation of harmful complexes in antigen excess of equivalence to antibody, and low levels of antitoxins might incompletely prevent toxic changes in blood vessels, predisposing them to penetration by harmful complexes.