Figure 3.

FcγRII expression analysis in B593. (A) Northern blot analysis of FcγRII expression in B593 compared with cell lines of hematopoietic origin. Total RNA (20 μg) was size-fractionated on an agarose gel and was blotted and sequentially hybridized with FcγRIIB (EC2/TM) and β-actin cDNA probes. After overnight exposure, very high level expression of 1.5- and 2.4-kb transcripts was detectable in B593 compared with the other cell lines. Jurkat and CEM do not normally express FcγRII, being of T-cell origin. (B) RT-PCR assay for characterization of FcγRII transcripts in B593. A primer pair overlapping the EC2, TM, and IC exons of A/C (immunoreceptor tyrosine-based activation motif Fc receptors) (Top) and FcγRIIB transcripts (ITIM receptor) (Middle), respectively, were used. The FcγRIIB specific primer pair generates a 541-bp b1 isoform-specific transcript and a 484-bp b2 isoform-specific transcript. RNA quality was verified by amplification of a 203-bp β-actin cDNA. FcγRII expression in U937 and Raji cell lines was concordant with previously described data concerning these cell lines (25, 33). Two bands (442 and 396 bp) observed in U937 correspond to alternatively spliced forms of A and/or C transcripts. B593 and B-EBV both express a single FcγRIIA/C transcript. An aberrant FcγRIIB expression profile is observed in B593: hyperexpression of the FcγRIIb2 specific transcript [indicated by b2 (Middle)].