Anti-FCRL4 monoclonal antibody, clone 3I6 [APC]

Recently identified Fc receptor-like (FCRL) molecules are new members of the immunoglobulin superfamily dominantly expressed by B cells. Although FCRL expression patterns have been studied in normal and malignant cells, their biological functions and roles remain to be clearly identified in humans. Research has particularly focused on FCRL gene polymorphisms in autoimmune diseases, however, their involvement in the pathogenesis of autoimmune diseases is an interesting field for investigation. In the present study, we have investigated the gene expression profiles of FCRL1, 2, and 4 in 2 common thyroid diseases, Hashimoto's thyroiditis (HT) and Graves' disease (GD). FCRL1, 2, and 4 expressions were determined in peripheral blood samples of 55 HT patients, 40 GD patients and equal numbers of normal subjects by quantitative real-time PCR. Our results showed downregulation of FCRL1 and upregulation of FCRL2 transcripts in both HT and GD groups compared to healthy counterparts. Overexpression of FCRL4 was observed only in GD patients compared to controls. A significant correlation was observed between all FCRL gene expression levels in HT patients. Only FCRL2 and 4 had a correlation in GD patients. In addition, FCRL1, 2, and 4 gene expressions showed no correlations with the level of anti-thyroid peroxidase antibody (anti-TPO) or anti-thyroglobulin (anti-Tg) antibody from patients' sera. In conclusion, expressions of activating or inhibitory FCRL1, 2, and 4 showed significant alterations in HT and GD patients compared to healthy subjects.

Chronic hepatitis C virus (HCV) infection is characterized by persistent B-cell activation, with enhanced differentiation and reduced proliferative ability. To assess the possible role of HCV in altering B-cell subset distribution, we examined ex vivo frequencies and B-cell inhibitory receptor expression in 37 chronic HCV-infected patients and 25 healthy donors (HD). In addition, we determined whether short-term exposure to culture-derived HCV (HCVcc) resulted in B-cell subset skewing and/or activation. There was a statistically significant increase in the frequencies of immature transitional, activated memory and tissue-like memory (TLM) B cells in HCV-infected patients compared with HD. We also found that the frequency of memory B cells correlated with serum HCV RNA levels. The proportion of B cells expressing the marker of exhaustion Fc receptor-like 4 (FcRL4) was generally low even though significantly higher in the patients' memory B-cell compartment compared with HD, and a positive correlation was found between the frequencies of the patients' TLM FcRL4+ B cells and serum alanine aminotransferase and histological activity index at liver biopsy. Exposure to cell-free HCVcc in vitro did not result in B-cell skewing but induced significant activation of naive, TLM and resting memory B cells in HCV-infected patients but not in HD, in whom cell-associated virus was an absolute requirement for activation of memory B cells. These findings provide corroborative evidence in favour of significant B-cell subset skewing in chronic HCV infection and in addition show that expression of exhaustion markers in selected B-cell subsets does not impair virus-induced B-cell activation.