Anti-Human IgHM monoclonal antibody, clone CS12

The protein Zfp318 is expressed during the transition of naive B cells from an immature to mature state. To evaluate its role in mature B cell functions, a conditional gene deficiency in Zfp318 was created and deleted in bone marrow lineages via Vav-Cre. B cell development was minimally altered in the absence of the protein, although transitional 2 (T2) B cell populations were depressed in the absence of Zfp318. Intriguingly, the analysis of IgM and IgD expression by maturing and mature naive B cells demonstrated an elevated level of IgM gene products and a virtual loss of IgD products. Transcriptome analysis of Zfp318-deficient B cells revealed that only two gene products showed altered expression in the absence of Zfp318 (Ighd and Sva), demonstrating a remarkable specificity of Zfp318 action. In the absence of Zfp318, Ighm/Ighd transcripts, which would normally encode IgM and IgD from heterogeneous nuclear RNA transcripts via alternative splicing, lack intron and exon sequences from the IgD (Ighd)-encoding region. This finding indicates that Zfp318, in a novel manner, functions by repressing recognition of the transcriptional termination site at the 3' end of the terminal IgM-encoding exon, allowing for synthesis of the complete Ighm/Ighd heterogeneous nuclear RNA.

A 67-year-old female with a history of colon cancer underwent colonoscopy. An 8 mm semi-pedunculated, friable, and ulcerated lesion of the ascending colon was removed completely using a hot snare. Immunohistochemical staining showed strong positivity for transcription factor binding to IGHM enhancer 3 (TFE-3) and was partially positive for Human Melanoma Black (HMB-45), consistent with a diagnosis of perivascular epithelioid cell tumor (PEComa). The patient underwent endoscopic submucosal dissection of the residual lesion in the ascending colon without complications. Here, we discuss the clinical and histopathologic characterizations that helped guide the diagnosis and management of this exceedingly rare entity.