Enhanced expression of Fc alpha receptor I on blood phagocytes of patients with gram-negative bacteremia is associated with tyrosine phosphorylation of the FcR-gamma subunit.
Sepsis caused by gram-negative bacteria is a common finding having high incidence and mortality. Fc alpha RI (CD89), a receptor for immunoglobulin A (IgA), has been shown to mediate bacterial phagocytosis, which might play a role in the pathogenesis of sepsis. In this study the expression and function of Fc alpha RI were analyzed on blood monocytes and neutrophils of patients with bacteremia. We found a marked increased in expression of the alpha- and gamma-subunits of the Fc alpha RI on both types of cells in patients with gram-negative bacteremia, but not in patients with gram-positive bacteremia. This increase was independent of serum IgA levels. Fc alpha RI M(r) was lower on cells from gram-negative patients than on cells from controls (50-65 kDa versus 55-75 kDa), despite a similar 32-kDa backbone, indicating altered glycosylation. Increased levels of Fc alpha RI on blood phagocytes correlated with enhanced serum IL-6 levels, but not with IFN gamma or TNF-alpha. FcR-gamma chain associated with Fc alpha RI was phosphorylated in patients neutrophils, indicating functional engagement of this receptor during gram-negative sepsis. Increased expression and activation of Fc alpha RI-gamma 2 complexes following gram-negative infections suggests its involvement in host defense against bacteria.
Chiamolera
M
M
Divisions of Emergency Medicine, University of São Paulo, São Paulo, Brazil.
Launay
P
P
Montenegro
V
V
Rivero
M C
MC
Velasco
I T
IT
Monteiro
R C
RC
D018806:APACHE; D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000818:Animals; D000911:Antibodies, Monoclonal; D015703:Antigens, CD / Q000097:blood / Q000235:genetics*; D016470:Bacteremia / Q000097:blood / Q000276:immunology*; D002648:Child; D005260:Female; D016905:Gram-Negative Bacterial Infections / Q000097:blood / Q000276:immunology*; D016908:Gram-Positive Bacterial Infections / Q000097:blood / Q000276:immunology; D006801:Humans; D015850:Interleukin-6 / Q000097:blood*; D008297:Male; D051379:Mice; D008875:Middle Aged; D019000:Phosphotyrosine / Q000378:metabolism*; D021122:Protein Subunits; D011961:Receptors, Fc / Q000097:blood / Q000235:genetics*; D017452:Receptors, IgG / Q000097:blood* / Q000737:chemistry; D012016:Reference Values; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism*
D000911:Antibodies, Monoclonal; D015703:Antigens, CD; C036832:Fc(alpha) receptor; D015850:Interleukin-6; D021122:Protein Subunits; D011961:Receptors, Fc; D017452:Receptors, IgG; D014409:Tumor Necrosis Factor-alpha; D019000:Phosphotyrosine