The differentiation antigen recognized by McAb 5C5-G1 is expressed on the surface of activated B cells

Objective: Since the homology between 2-450bp of 5C5 cDNA (GenBank accession number U25041) and 560-1008bp of HSMRP17 mRNA (GenBank accession number X79685) reaches 95% and protein MRPL12 encoded by HSMRP17 mRNA is expressed and accumulated during the G1 phase of growth-stimulated cells, the objective of the experiment is to estimate if the proteins encoded by the two genes are the same. Methods: The indirect immunofluorescence staining was done on several human B cell lines with McAb 5C5-G1 and examination was carried out under a laser scanning confocal microscope. Results: It was observed that the protein recognized by McAb 5C5-G1 was only found on the membrane of 3D5 cells, and not in the cytoplasm, while MRPL12 was only found in mitochondria. Besides, the reaction between human pro-B cell line Nalm-6 and McAb 5C5-G1 was negative, the reaction between Daudi, 3D5 cells and the McAb was strongly positive, and SKW-6 cell was weekly positive in staining with the McAb. Conclusions: 1) It is suggested that 5C5 cDNA and HSMRP17 mRNA are not the same; 2) The expression of the differentiation antigen recognized by the McAb is changing during B cell differentiation.