Immunohistochemical demonstration of CD 23 expression on lymphocytes in rheumatoid

The leucocyte antigen CD23 is expressed by B lymphocytes following activation by a number of stimuli and functions as an IgE receptor, and in its soluble form, as a putative B cell growth factor. The expression of CD23 on the surface of lymphocytes in paraffin wax sections of synovial biopsy specimens was studied using a novel mouse monoclonal antibody, BU38. Specimens were investigated from nine cases of rheumatoid arthritis, six cases of osteoarthritis, and eight cases of chronic inflammation in articular and non-articular tissues. CD23 was expressed on a high proportion of lymphocytes in all forms of chronic inflammation andwas not specific for rheumatoid arthritis. It may be a characteristic feature of any chronic inflammatory response. As CD23 was found on the surface of lymphocytes in many cases of these arthritides, sCD23 in serum or synovial fluid may yet prove a useful marker for the severity of the inflammatory infiltrate. Department of Histopathology, East Birmingham Hospital, Bordesley Green East, Birmingham B9 5ST E A Hellen D C Rowlands J Crocker Department of Immunology T T Hansel Department of Rheumatology, University of Birmingham Medical School G D Kitas Correspondence to: Dr J Crocker Accepted for publication 23 October 1990 Rheumatoid arthritis is a chronic inflammatory disease which predominantly affects synovial tissues, resulting in irreversible articular damage and loss of function. Most patients with rheumatoid arthritis have serum rheumatoid factors consisting of immunoglobulins with specificity for the Fc fragment of IgG. Synovial lymphocytes have the capacity to produce rheumatoid factors, and the rheumatoid synovium is infiltrated with activated B and T cells.'2 A lymphocytic infiltrate is also seen, however, in other chronic synovitides.34 Although the aetiology of rheumatoid arthritis is unknown, there is an association with HLA DR4,"6 and a defect in cellular immunity with abnormal production of and response to cytokines has been postulated.78 Certain infectious agents including Epstein Barr virus (EBV) have also been implicated in the pathogenesis of the disease."' The low affinity IgE receptor (CD23) is a 45 kilodalton molecule expressed on IgM/IgD bearing B lymphocytes following activation,'2 13 as well as on a number of other cell types including follicular dendritic cells and Langerhans' cells.'2 1416 CD23 expression on B lymphocytes is particularly increased following infection by EBV,'7 but also occurs after activation by a number of other stimuli such as interleukin 4 and so is not specific to EBV infection.'2 CD23 also exists in a 25-30 kilodalton soluble form (sCD23) that is secreted or can be formed by cleavage of surface CD23.1' This sCD23 has been suggested to have autocrine B lymphocyte growth factor activity,'920 although gene cloned sCD23 does not have this property.2' In this study we investigated the expression of CD23 by lymphocytes in paraffin wax embedded synovial biopsy specimens from patients with rheumatoid arthritis and osteoarthritis. Several specimens of other tissues showing chronic inflammation were also studied. A novel mouse monoclonal antibody, BU38, with the particular advantage of being able to visualise CD23 in paraffin wax sections" was used.