A PGK-neomycin resistance cassette was inserted into exon 4 that resulted in an in-frame termination codon upstream of the ICE cleavage site. The authors predict that the receptor-binding domain of the protein would not be translated. Northern blot analysis detected no transcripts in LPS-stimulated peritoneal exudate cells from homozygous mice. Pulse-chase labeling and immunoprecipitation studies of thioglycollate-elicited PEC demonstrated that no detectable protein was present in homozygous mice. ELIZA analysis of ATP-treated PEC also did not detect protein produced by this allele.