Determination of soluble CD21 as a parameter of B cell activation

Abstract

SUMMARYIn this study we established a novel solid-phase immunoassay for CD21 using the time-resolved tluoresccnccof lanthanidechclates. The capture assay was able to detect concentrations ofas low as IOOpgofCD2l antigen per millil[trcor.saniple and was used for quantitative determination orCD21 in lysatcs of different cell lines as well as in patient serum specimens. CD21 was measured in lysates of tonsils and eell lines of B, T cell and myelomonoeyte lineage, and appeared to eonsist ofmonomeric aniigen under the detergent conditions used. Elevated levels of soluble CD2I were observed in serum of patients with Epstein Barr virus (EBV) infection, a disease known to be associated with polyclonal B cell activation, and in infection with ihe lymphotropie rubella virus. Significantly increased levels were also found in malignancies whieh are associated with EBV, In patients with nasopharyngeal carcinoma (NPC). a correlation with the litre of EBV-specific IgA was observed, thus supporting a possible role of soluble CD2I as a marker for disease activity in certain malignancies. Our data suggest that measurement of soluble CD21 could serve as a marker for activation of the immune system and diseases involving the B cell lymphoid system. Possible mechanisms and functions of soluble CD21 are discussed.

Pitfalls in the measurement of soluble forms of cell surface receptors

“…As the interesting investigation by Huemer et al shows, increased amounts of sCR2 are found in the serum of patients with infectious mononueleosis and rubella, two diseases due to lymphotropic viruses and associated with a marked lymphoproliferation [32]. It was also confirmed that raised serum levels of sCR2 are found in B cell chronic lymphocytic leukaemia.…”

“…In this issue Huemer et at. describe an ingenious new antigen-capture/fluorescent chelate assay for sCR2 whieh detects concentrations of monomeric antigen as low as 0-1 ng/ml [32]. They find a discrepancy in the absolute values of sCR2 obtained by their technique compared with reported HA results.…”

Decreased levels of sCD21 and sCD23 in blood of patients with systemic-juvenile arthritis, polyarticular-juvenile arthritis, and pauciarticular-juvenile arthritis

“…In B lymphocytes, CD21 ampliWes the signal through the B-cell receptor [14], and in turn, B-cell receptor activation induces CD21 shedding [15]. The clinical signiWcance of sCD21 is shown by higher levels in sera of patients with EBV infection and lymphoblastoid tumors [16] and lower levels in autoimmune diseases like RA, SLE, Sjoegren's syndrome, and antiphospholipid syndrome [15,[17][18][19][20]. sCD21 activates monocytes through binding to membrane CD23 and leads to degranulation of basophils upon crosslinking [21].…”

Serum levels of soluble CD21 in patients with systemic sclerosis

“…This complex amplifies the signal transmitted through the B-cell receptor by specific antigen and thereby reduces the threshold of antigen necessary to initiate cell proliferation [6,7]. CD21 is shed from the surface of the cell and is found circulating in plasma [8][9][10]. Soluble CD21 (sCD21) activates monocytes through binding to membrane CD23.…”