Anti-phosphatidylcholine antibodies in patients with brucellosis.

An indirect ELISA was adapted to measure individual classes of anti-phosphatidylcholine (PC) antibodies in patients with brucellosis; a comparison was made with patients with other infectious diseases and healthy human controls. Immunoconjugates of alpha, gamma or mu chain specificity were used. The results were compared with those of conventional tests for brucella antibodies, Rose Bengal, microagglutination (MAT) and Coombs tests, as well as with VDRL. The results indicated that although all sera from patients with brucellosis were VDRL negative, 97% of them (30 of 31) had higher levels of IgA or IgG anti-PC antibodies than the healthy control group. The IgM anti-PC antibodies isotype was not discriminatory between both groups. Seven sera (19%) from patients with other infections had values of IgG anti-PC higher than those of the healthy group; three of them were VDRL positive. The mean ELISA values of IgG and IgA anti-PC (serum diluted 1 in 1600) in the brucellosis and healthy groups were: IgG, 0.80 SEM 0.17 versus 0.23 SEM 0.10; and IgA, 0.86 SEM 0.26 versus 0.35 SEM 0.15. The sensitivity and specificity for the ELISA-PC were: IgG, 96.8% and 96.5%, respectively; IgA, 90.3% and 89.7%, respectively. Only one of 14 individuals clinically cured from brucellosis had significant IgG anti-PC antibodies. In contrast, all of these patients gave positive values in the conventional test for brucellosis. No correlation was found between the serum levels of IgA, IgG anti-PC by ELISA-PC and the results of the MAT or Coombs tests.