Biochemical nature and topographic localization of epitopes defining four distinct CD45 antigen specificities. Conventional CD45, CD45R, 180 kDa (UCHL1) and 220/205/190 kDa.

The biochemical nature and relative topographic localization of Ag determinants recognized on CD45 molecular complex by mAb defining four distinct Ag specificities (conventional CD45, CD45R, 180 kDa and 220/205/190 kDa) have been investigated. These Ag specificities display a differential biochemical, cellular, and histochemical distributions and are important in the definition of CD4-positive complementary functional T cell subsets and/or distinct stages of thymic maturation. Protease treatment of either CD45-positive cells or purified CD45 molecules revealed that both conventional CD45 and 180-kDa (UCHL1 epitope) Ag specificities are defined by epitopes present on a protease-resistant domain which is internal to the protease-sensitive epitopes defining both CD45R and 220/205/190-kDa Ag specificities. In addition, it is shown that carbohydrate moieties are contributing to the epitopes recognized by both the anti-180-kDa UCHL1 and the anti-220/205/190-kDa mAb. Neuraminidase treatment, which cleaves sialic acids either from N- or O-linked oligosaccharides, abrogated the reactivity of both mAb. However, N-glycanase treatment, which selectively cleaves N-linked sugars, did not affect the recognition of these two epitopes. Thus, these results demonstrate that the Ag determinants recognized by the UCHL1 and the anti-220/205/190-kDa mAb, which are topographically unrelated, are associated with sialic acids from O-linked-type oligosaccharides, emphasizing the contribution of carbohydrates to the Ag heterogeneity of CD45 molecular complex.