B-cell origin of cold agglutinins

B CELL IMMUNOBIOLOGY IN DISEASE: Evolving Concepts from the Clinic

The pathogenic roles of B cells in autoimmune diseases occur through several mechanistic pathways that include autoantibodies, immune complexes, dendritic and T cell activation, cytokine synthesis, chemokine-mediated functions, and ectopic neolymphogenesis. Each of these pathways participate to different degrees in autoimmune diseases. The use of B cell-targeted and B cell subset-targeted therapies in humans is illuminating the mechanisms at work in a variety of human autoimmune diseases. In this review, we highlight some of these recent findings that provide insights into both murine models of autoimmunity and human autoimmune diseases.

Cold Agglutinin Disease and Cryoglobulinemia

Cold agglutinin disease is a form of direct, extravascular, antiglobulin-positive hemolysis. In vivo, immunoglobulin (Ig) M fixes complement molecules to the red cell membrane. Successive passages through the mononuclear phagocyte system result in loss of red cell membrane. The resultant spherocytes lose resiliency and are ultimately lost from the circulation extravascularly. The high concentration of complement molecules on the red cell surfaces makes this syndrome resistant to the standard therapies for immune-mediated hemolysis. Rituximab has been reported to reduce the severity of hemolysis. Type II cryoglobulins are composed of a monoclonal IgM and a polyclonal IgG. These complexes have rheumatoid factor activity and can produce immune-complex vasculitis. The target organs are the skin, nerves, kidney, liver, and joints. More than 80% of patients have evidence of hepatitis C infection. Interferon and interferon plus ribavirin have been shown to produce serologic responses. When vasculitis is active, corticosteroids are often required to permit healing of ulcers in the skin or to treat the membranoproliferative glomerulonephritis that is seen, thereby preventing loss of renal function. Rituximab therapy has been found to be effective in mixed cryoglobulinemia, with decreases in cryoglobulin values and improvement in complement values.

Pathogenic roles of B cells in human autoimmunity; insights from the clinic

The pathogenic roles of B cells in human autoimmune diseases involve a multitude of mechanistic pathways and include the well-established contributions of autoantibodies and immune complexes that induce local inflammatory reactions and tissue destruction. Recent results using several novel B cell-directed therapies have provided new insights into additional roles of B cells in human autoimmunity. In this review, we will highlight some of these studies and discuss how clinical insights parallel murine models of normal immunity and autoimmunity.

Favourable response to therapy with the anti-CD20 monoclonal antibody rituximab in primary chronic cold agglutinin disease

The 'primary' form of chronic cold agglutinin disease is a clonal B-cell lymphoproliferative disorder that is notoriously difficult to treat with drugs, including corticosteroids, alkylating agents, alpha-interferon and purine analogues. We performed a small, open, uncontrolled, prospective study to evaluate the effect of therapy with the monoclonal anti-CD20 antibody rituximab. Six patients with clonal CD20(+)kappa(+) B-cell proliferation received seven courses of rituximab 375 mg/m(2), d 1, 8, 15, and 22. One patient achieved a complete response. Four partial responses were observed, including a response to re-treatment in one patient. Two patients were categorized as non-responders. Haemoglobin levels increased by a median of 4.1 g/dl in the total group and 4.7 g/dl in the responders, who also experienced a substantial improvement of clinical symptoms. The treatment was well tolerated. We discuss the effect of rituximab therapy compared with other treatment options, and try to explain why two individual patients did not respond. Despite the small numbers, the results are very encouraging. Further studies of rituximab therapy for chronic cold agglutinin disease are warranted.