Binding of C-reactive protein (CRP) by human peripheral blood lymphocytes in vivo

Antigenicity of C-reactive protein (CRP) on the surface of human lymphocytes was investigated by use of indirect immunofluorescence technique with anti-CRP antibodies. CRP on the lymphocyte surface (sd-CRP) belongs to two different categories: i) CRP produced by lymphocytes and inserted into cell membrane (s-CRP), ii) CRP produced primarily by the liver and bound by the lymphocytes (sb-CRP) in calcium-dependent manner. In human peripheral blood of healthy donors approximately 2.5% of lymphocytes expressed membrane CRP (s-CRP) and 1.5% of lymphocytes bound CRP in calcium-dependent manner (sb-CRP). Percentage of s-CRP lymphocytes increased in patients with rheumatoid arthritis, while population of sb-CRP lymphocytes did not change significantly, except cases where serum CRP concentration reached more than 50 micrograms/ml. Thus, it can be concluded that CRP is bound to the distinct population of lymphocytes, bearing specific membrane receptors.