Development of an ELISA assay for soluble CD35 (C3b/C4b receptor): high levels of soluble CD35 in LE-positive patients with hematological malignancies

B-cell antigens within normal and activated human T cells

In this study we compared cell surface staining for human peripheral blood lymphocyte (PBL) CD antigens by flow cytometry, with staining obtained following permeabilization of PBL using the Cytoperm method (Serotec). Six CD antigens (CD20, CD21, CD22, CD32, CD35 and major histocompatibility complex class II antigen) normally found on the surface of B cells, were also found to be expressed within T cells. We also showed, by immunoelectron microscopy, that these inappropriately expressed ('occult') CD antigens are located within cytoplasmic vesicles or within the rough endoplasmic reticulum. Following in vitro activation of T cells a distinct increase in expression of all of these cytoplasmic antigens was observed but staining at the cell surface was, by comparison, weak. We therefore propose that up-regulation of various B-cell CD antigens occurs within the cytoplasm of T cells following activation and that these antigens may be synthesized and released into the fluid-phase as soluble immunoregulatory molecules.

Rapid purification of human complement receptor type 1 (CD35, CR1)

We established a rapid purification procedure for complement receptor type 1 (CR1, CD35). Human erythrocyte stromata were solubilized, and the extract was directly applied to a Red-Sepharose column. The eluate was diluted 2-fold, then subjected to an immunoaffinity column, anti-CR1 (named 31R)-conjugated to Sepharose. More than 50% of CR1 was recovered with purity of > 90%. The CR1 preparation showed sufficient cofactor activity for factor I as compared to that prepared by the conventional method. Since 31R recognizes a single epitope in CR1 including its rare variants and soluble forms, this method will allow us to recover with high efficiency these forms of CR1 which have been detected especially in some disease states.