B lymphocyte subsets in Hashimoto's thyroiditis

Breakage of B cell tolerance and autoantibody production in anti-erythrocyte transgenic mice

In summary, there are two pathways for activation of peritoneal B-1 cells in HL mice: T cell-dependent and T cell-independent pathways. In both pathways, IL-10 is suggested to play an important role (Fig. 1). We have not yet known what type of cells secrete IL-10 by and whether other soluble factors are involved in each pathway. These questions are to be elucidated by further studies on HL mice.

Synthesis of anti-acetylcholine receptor antibodies by CD5- B cells from peripheral blood of myasthenia gravis patients

An increased frequency of CD5+ B cells (or, according to a new nomenclature, B1 cells) has been detected in the peripheral blood of a proportion of patients with myasthenia gravis (MG), as in some other autoimmune diseases. To elucidate the pathogenic significance of this B-cell subset in myasthenia gravis, mononuclear cells from the peripheral blood of six MG patients were separated into T and B lymphocytes by a magnetic cell separation procedure employing superparamagnetic microbeads (MACS). Subsequently, the B-cell fraction was depleted of CD5+ B cells in a second separation. The resulting purified CD5- B-cell fraction was cultured alone or with the addition of autologous T cells. Anti-acetylcholine receptor (AChR) synthesis by CD5- B cells in cultures with T cells was significantly increased by pokeweed mitogen (176 +/- 130 fmol/ml per week/2 x 10(5) B cells) compared with unfractionated cells (75 +/- 101) or CD5- B cells alone (19 +/- 4). These results demonstrate that in MG anti-AChR are synthesized, at least in part, by CD5- B cells which are dependent on T cells. Although this does not exclude the existence of AChR-specific CD5+ B cells, it provides evidence against a pivotal role of this B-cell subset in anti-AChR synthesis.

B-1 cells in systemic autoimmune responses: IgM+, Fc epsilon Rdull B cells are lost during chronic graft-versus-host disease but not in murine AIDS or collagen-induced arthritis

The potential role of B-1 cells (i.e. the CD5+ B cell and "sister" B cell subsets) in autoimmunity is controversial. CD5+ B cells have been shown to secrete antibodies of similar specificity as those found in many systemic autoimmune diseases; in addition, increases in CD5+ B cell frequency have been reported in patients suffering from rheumatoid arthritis, Sjögren's syndrome, myasthenia gravis, insulin-dependent diabetes mellitus and Hashimoto's thyroiditis. Whether these increases are due to expansion of B-1 lineage cells in the human or due to activation-induced expression of CD5 by conventional B cells is unclear. In the present study, we used three murine models of systemic autoimmunity: murine acquired immunodeficiency syndrome (MAIDS), chronic graft-versus-host disease (cGvHD), and collagen-induced arthritis (CIA) to determine whether increases in B-1 cell frequency are universally seen in models of autoimmunity which are mechanistically distinct. In contrast to the aforementioned human systemic autoimmune diseases which exhibit an increase in CD5+ B cell frequency, the percentage of CD5+ B cells declined in all three murine models of systemic autoimmune disease. Even though there was a decrease in the frequency of CD5+ B cells there was no change in the actual number of CD5+ B cells. Thus, the apparent decline in CD5+ B cell frequency was due to increases in either T cells, conventional Fc epsilon R+ B cells, or both. The only actual decline in a B cell subset was the loss of IgM+, Fc epsilon Rdull cells in both the spleen and peritoneal cavity of mice undergoing a chronic graft-versus-host reaction. Therefore, our data suggests that expansion of the B-1 subset does not occur as a general feature of murine systemic autoimmune disease. These observations, consistent with previous studies of Ig gene usage in autoreactive antibodies, support the view that expansion and differentiation of the CD5+ B cell subset is not a central event leading to autoantibody production.

CD5-positive B cells in type 1 (insulin-dependent) diabetic children

We have measured CD5+ B cell levels in the peripheral blood of 35 type 1 (insulin-dependent) diabetic children, aged 1.1-21.2 years (10.7 +/- 4.6 years). Patients were divided into two groups according to disease duration (group I < 6 months and group II > 1.5 years). Group I included 18 patients and group II 17 patients. Thirty-nine healthy subjects, comparable for age and sex, served as controls. CD5+ B cells were identified by double immunofluorescence staining with rhodamine-conjugated rabbit anti-human immunoglobulin and with a mouse anti-CD5 monoclonal antibody revealed by a fluorescein-conjugated goat anti-mouse immunoglobulin. We found that CD5+ B cell levels (expressed as percentages of peripheral blood B lymphocytes) were significantly higher in group I (median 24; range 4-48) than in controls (median 14; range 0-36, P < 0.001) and in group II (median 4; range 0-20, P < 0.001). A follow-up study of 12 group I patients showed a significant decline in CD5+ B cell levels. The data obtained in our diabetic patients suggest that CD5+ B cells are expanded in the early phase of type 1 diabetes mellitus and may play a role in the autoimmune process of the disease.