CD45 autoantibodies mediate neutralization of activated T cells from lupuspatients through anergy or apoptosis

The objectives were to provide estimates of the prevalence of autoantibody (Ab) directed to CD45 in lupus patients, identify the target autoantigen(s) , and determine the ability of such reactivity to mediate neutralization of T lymphocytes. Sera from 64 patients were studied using 2 assays: Western blot and an ELIS A with CD45 eluted from 3 cell lines as antigen (U937, Jurkat and Daudi). T he role of carbohydrate specificity was investigated using enzyme digestion of blotted glycans, competition with sugars, and inhibition with lectins. Apoptosis was studied through annexin V binding, and cell cycle analysis us ing the propidium iodide method. AutoAb to CD45 were detected in 16/64 sera (25%) by Western blot, and 21/32 sera (66%) found positive in the ELISA. CD45 purified from Daudi cells was identified in the ELISA, but not in the blot. AutoAb were of the IgM and t he IgG isotypes, but not specific for a particular cell type or CD45 isofor m: 2 dominant specificities were recognized, one against p180, and another against high MW isoforms. Neuraminidase-induced enhancement of reactivity, together with the inhibitory effect of N-acetyl galactosamine and Dolichos diflorus lectin suggest that the epitopes are carbohydrates. AutoAb which w ere specific for activated CD4+ T cells triggered the annexin V binding, an d, in 2 of 4 cases, lymphocytes underwent apoptosis. In conclusion, carbohydrate conformational epitopes may be important as tar get antigens, and some CD45 autoAb have the capacity to neutralize activate d T cells through anergy or apoptosis.