Anti-CD5 monoclonal antibody, clone M28G23 [PerCP/Cy5.5®]

Background: Anti-carbohydrate antibody responses, including those of anti-blood group ABO antibodies, are yet to be thoroughly studied in humans. Because anti-ABO antibody-mediated rejection is a key hurdle in ABO-incompatible transplantation, it is important to understand the cellular mechanism of anti-ABO responses. We aimed to identify the main human B cell subsets that produce anti-ABO antibodies by analyzing the correlation between B cell subsets and anti-ABO antibody titers. Methods: Blood group A-binding B cells were analyzed in peritoneal fluid and peripheral blood samples from 43 patients undergoing peritoneal dialysis and 18 healthy volunteers with blood group B or O. The correlation between each blood group A-specific B cell subset and anti-A antibody titer was then analyzed using Pearson's correlation analysis. Results: Blood group A-binding B cells were enriched in CD27(+)CD43(+)CD1c(-) B1, CD5(+) B1, CD11b(+) B1, and CD27(+)CD43(+)CD1c(+) marginal zone-B1 cells in peripheral blood. Blood group A-specific B1 cells (P=0.029 and R=0.356 for IgM; P=0.049 and R=0.325 for IgG) and marginal zone-B1 cells (P=0.011 and R=0.410 for IgM) were positively correlated with anti-A antibody titer. Further analysis of peritoneal B cells confirmed B1 cell enrichment in the peritoneal cavity but showed no difference in blood group A-specific B1 cell enrichment between the peritoneal cavity and peripheral blood. Conclusions: Human B1 cells are the key blood group A-specific B cells that have a moderate correlation with anti-A antibody titer and therefore constitute a potential therapeutic target for successful ABO-incompatible transplantation.

Secondary cutaneous involvement by mantle cell lymphoma (MCL), an uncommon aggressive B-cell malignancy, predominantly involves the dermis, with few reports of pannicular involvement. Lymphocytic infiltration of subcutaneous tissue is associated with inflammatory panniculitides and certain T-cell lymphomas, primarily subcutaneous panniculitis-like T-Cell lymphoma (SPTCL), which is characterized by rimming of adipocytes by tumor cells. We report the case of a 69-year-old man with a history of systemic nodal MCL who presented with subcutaneous nodules on his lower extremities after receiving multi-agent chemotherapy. Biopsies showed a dense infiltrate of atypical, mitotically active, monomorphic, medium-sized lymphoid cells in the subcutaneous fat with prominent rimming of the adipocytes by the tumor cells. These features were not morphologically typical of MCL. Immunohistochemistry showed these cells to be CD20+, CD5+ B-cells with strong cyclin D1 expression; fluorescence in situ hybridization (FISH) analysis was positive for t(11;14)(q13;32), confirming the diagnosis of secondary cutaneous involvement of MCL. This represents an exceptional report of cutaneous MCL presenting clinically and histologically with a panniculitis-type pattern and adipocyte rimming, histomorphologically mimicking SPTCL. Noteworthy examples, such as this report, support the practice of utilizing clinical correlation, immunohistochemistry, and/or molecular cytogenetics to confirm the diagnosis of any case suspicious for cutaneous lymphoma.