Anti-Cytokeratin High Molecular Weight monoclonal antibody, clone 35βE13

The contact system is composed of factor XII (FXII), prekallikrein (PK), and cofactor high-molecular-weight kininogen (HK). The globular C1q receptor (gC1qR) has been shown to interact with FXII and HK. We reveal the FXII fibronectin type II domain (FnII) binds gC1qR in a Zn2+-dependent fashion and determined the complex crystal structure. FXIIFnII binds the gC1qR trimer in an asymmetric fashion, with residues Arg36 and Arg65 forming contacts with 2 distinct negatively charged pockets. gC1qR residues Asp185 and His187 coordinate a Zn2+ adjacent to the FXII-binding site, and a comparison with the ligand-free gC1qR crystal structure reveals the anionic G1-loop becomes ordered upon FXIIFnII binding. Additional conformational changes in the region of the Zn2+-binding site reveal an allosteric basis for Zn2+ modulation of FXII binding. Mutagenesis coupled with surface plasmon resonance demonstrate the gC1qR Zn2+ site contributes to FXII binding, and plasma-based assays reveal gC1qR stimulates coagulation in a FXII-dependent manner. Analysis of the binding of HK domain 5 (HKD5) to gC1qR shows only 1 high-affinity binding site per trimer. Mutagenesis studies identify a critical G3-loop located at the center of the gC1qR trimer, suggesting steric occlusion as the mechanism for HKD5 asymmetric binding. Gel filtration experiments reveal that gC1qR clusters FXII and HK into a higher-order 500-kDa ternary complex. These results support the conclusion that extracellular gC1qR can act as a chaperone to cluster contact factors, which may be a prelude for initiating the cascades that drive bradykinin generation and the intrinsic pathway of coagulation.

Desmoplastic small round cell tumor (DSRCT) is a rare malignant mesenchymal neoplasm that typically affects young patients and presents as large intraabdominal masses. We report a rare case of parotid gland DSRCT in a 38-year-old man. The tumor cells were large sized and form irregular nests embedded in abundant desmoplastic stroma. Immunohistochemically, the tumor cells were positive for cytokeratin, GATA3, p40, and p63. Working differential diagnosis included squamous cell carcinoma, myoepithelial carcinoma, hyalinizing clear cell carcinoma, NUT (nuclear protein of the testis) carcinoma, and adamantinoma-like Ewing sarcoma. The characteristic morphologic features and presence of EWSR1-WT1 gene fusion are diagnostic of DSRCT. Salivary gland DSRCT is an exceedingly rare entity, with only 6 cases reported in the literature.