Identification of Fc alpha receptor (CD89) isoforms generated by alternative splicing that are differentially expressed between blood monocytes and alveolar macrophages.
One of the hallmarks of mucosal-host defense is the clearance of inhaled Ags by alveolar macrophages (AM) through interactions of IgA Abs and IgA Fc receptors (Fc alpha R). AM constitutively expressed Fc alpha R at lower levels than freshly isolated and in vitro-differentiated monocytes as determined by immunofluorescence using four anti-Fc alpha R mAb. SDS-PAGE analysis of iodinated cell surface proteins revealed that Fc alpha R on AM has an Mr of 50 to 65 kDa, slightly lower than that on monocytes (55-75 kDa). Treatment of AM Fc alpha R by N-glycanase gave rise to a protein core of 28 KDa, smaller than the 32-kDa backbone of blood monocytes. AM Fc alpha R molecules were unaffected by phosphatidylinositol-phospholipase C treatment. Fc alpha R transcripts were analyzed by reverse transcription-PCR using primers in the 5' and 3' regions of a U937 Fc alpha R cDNA. Three transcripts were amplified, cloned, and sequenced from AM and/or monocyte mRNA, the full length Fc alpha R and two alternatively spliced products corresponding to deletions of 66 and 288 nucleotides in the portion coding for the extracellular domain; they were named Fc alpha R a.1, a.2, and a.3, respectively. These PCR products were transcribed and translated in vitro into three proteins (Mr 32, 30, and 22 kDa, respectively), in which the 32- and 30-kDa species were immunoprecipitated by an anti-Fc alpha R mAb. The predicted size of the protein encoded by the Fc alpha R a.2 transcript without the leader peptide is Mr approximately 27,400, a value that is consistent with the Mr of AM Fc alpha R backbone. These results indicate that AM express at their surfaces a protein product of an alternatively spliced Fc alpha R transcript, the Fc alpha R a.2 isoform, that might have physiologic relevance in IgA-mediated host defense at mucosal sites.
Patry
C
C
INSERM U25, Necker Hospital, Paris, France.
Sibille
Y
Y
Lehuen
A
A
Monteiro
R C
RC
D017398:Alternative Splicing; D000818:Animals; D000911:Antibodies, Monoclonal; D015703:Antigens, CD / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D001483:Base Sequence; D017931:DNA Primers / Q000235:genetics; D018076:DNA, Complementary / Q000235:genetics; D015870:Gene Expression; D006801:Humans; D018928:Immunity, Mucosal; D066298:In Vitro Techniques; D016676:Macrophages, Alveolar / Q000276:immunology*; D051379:Mice; D008969:Molecular Sequence Data; D009000:Monocytes / Q000276:immunology*; D016133:Polymerase Chain Reaction; D014176:Protein Biosynthesis; D011961:Receptors, Fc / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D012689:Sequence Homology, Nucleic Acid; D014158:Transcription, Genetic
D000911:Antibodies, Monoclonal; D015703:Antigens, CD; D017931:DNA Primers; D018076:DNA, Complementary; C036832:Fc(alpha) receptor; D011961:Receptors, Fc