Fc and complement receptor (CR1 and CR3) expression on neonatal human polymorphonuclear leukocytes

Expression of Fc(gamma)r1 (CD64) on polymorphonuclear leucocytes during progression to acquired immunodeficiency syndrome in perinatally human immunodeficiency virus-infected children

CD64, the high-affinity receptor in the family of FCgamma receptors, is not expressed constitutively in polymorphonuclear leucocytes (PMN). CD64 is expressed by PMNs in the late stages of human immunodeficiency virus (HIV) infection in adults. We followed the expression of CD64 on PMNs in perinatally HIV-infected children during disease progression. Peripheral blood leucocytes (PBL) from 45 perinatally HIV-infected paediatric patients and 13 healthy age-matched controls were analysed using cytofluorimetry after reaction with a fluorophore-labelled monoclonal antibody (MoAb) to CD64. In parallel, we examined the expression of CD32, CD16, CD11b and the human neutrophil-specific BH2-Ag using fluorophore-labelled MoAbs. We found that up to 79.5% of the PMNs in children in class C3 express CD64. Most importantly, we observed a continuous and significant increase in the appearance of CD64+ PMNs as a function of CDC classification (P < 0.001) but no changes in the expression of CD32, CD16, CD11b and BH2-Ag. This suggests that following the expression of CD64 on PMNs can be useful in evaluating the progression of HIV infection in perinatally HIV-infected children.

Flow cytometric analysis of group B streptococci phagocytosis and oxidative burst in human neutrophils and monocytes

Group B streptococci (GBS) are a major cause of meningitis and septicemia in neonates and numerous invasive diseases in adults. Host defense against GBS infections relies upon phagocytosis and killing by phagocytic cells. To better understand the importance of this defense mechanism a flow cytometric assay was developed to study phagocytosis and oxidative burst of leukocytes stimulated by bacteria. GBS labeled with fluorescein isothiocyanate were used for phagocytosis experiments and the extracellular fluorescence was quenched by ethidium bromide to differentiate intracellular from extracellular bacteria. The intracellular oxidative burst was determined by using 2',7'-dichlorofluorescein diacetate to measure hydrogen peroxide production and hydroethidine for superoxide anion production. We found that for GBS serotypes Ia, Ib/c, II, and III phagocytosis was greater in neutrophils than monocytes. Hydrogen peroxide production and superoxide anion production were also greater for neutrophils than monocytes in all serotypes tested. A comparison of seven type III strains revealed greater phagocytosis and superoxide anion production by neutrophils than monocytes but no difference in hydrogen peroxide production. Therefore, monocytes react similarly as neutrophils in response to GBS but at a reduced level. This methodology of measuring both phagocytosis of GBS and oxidative burst simultaneously in neutrophils and monocytes should be very useful in further studies on the importance of factors such as complement and IgG receptors for the killing of bacteria.

Fc gamma RI and Fc gamma RIII on polymorphonuclear leucocytes in cord blood

Fc gamma RI and Fc gamma RIII expression on polymorphonuclear leucocytes in cord blood from seven normal infants was investigated by flow cytometry. Fc gamma R expression on fresh polymorphonuclear leucocytes in whole blood samples and in blood samples incubated with or without interferon gamma (IFN-gamma) for 48 hours was also studied. The percentage of Fc gamma RIII positive polymorphonuclear leucocytes in cord blood (73.3%) was significantly lower than that in adult controls (95.9%). The mean fluorescence intensity of Fc gamma RIII was significantly increased on cord polymorphonuclear leucocytes by the incubation with IFN-gamma. Fresh cord polymorphonuclear leucocytes expressed only a small amount of Fc gamma RI as adult polymorphonuclear leucocytes. The percentage of Fc gamma RI positive polymorphonuclear leucocytes induced with IFN-gamma was significantly higher in cord blood (62.3%) than in adult controls (30.3%). It is possible that decreased expression of Fc gamma RIII is a factor in the susceptibility of newborns to infection. High expression of Fc gamma RI stimulated with IFN-gamma in neonates could have a compensatory role against decreased immunological function.

Diversity in regulation of adhesion molecules (Mac-1 and L-selectin) in monocytes and neutrophils from neonates and adults

The surface expression and regulation of the adhesion promoting glycoproteins Mac-1 and L-selectin was measured on monocytes and neutrophils from neonates and adults. A significant decrease in Mac-1 up regulation on both monocytes and neutrophils was found in neonates after both high (10(-7)M) and low (10(-9)M) concentrations of the chemotactic factor N-formyl-methionyl-phenylalanine (FMLP). A significant difference was obtained after incubation for five minutes, which was further enhanced after incubation for 15 minutes. Factors related to bacterial infections, lipopolysaccharides, activated sera (C5a), and aggregated IgG induced an impaired Mac-1 up regulation on both monocytes and neutrophils from neonates compared with adults. The expression of L-selectin was significantly lower on neutrophils from neonates and was less down regulated upon stimulation with a low concentration (10(-12)M) of FMLP. On monocytes from neonates, the expression and down regulation of L-selectin did not differ from monocytes from adults. Mode of delivery did not influence the regulation of Mac-1 and L-selectin in neonates. Diversity in expression and regulation of Mac-1 and L-selectin on monocytes and neutrophils may contribute to the increased susceptibility to infections observed in neonates.

Opsonin-independent phagocytosis of group B streptococci: role of complement receptor type three

The role of complement receptor type 3 (CR3) in nonopsonic recognition of group B streptococci (GBS) by macrophages was investigated. Monoclonal anti-CR3 (anti-Mac-1) inhibited phagocytosis of GBS strains by as much as 50% in serum-free cultures of both mouse peritoneal macrophages and the macrophage cell line PU5-1.8. GBS uptake was unaffected by the presence of anti-C3 or salicylhydroxamate, an inhibitor of the covalent binding reaction of C3. Soluble antibodies to LFA-1 or to the common beta-chain (CD18) of the LFA-1/CR3/p150,95 family of cell adhesion molecules did not inhibit GBS uptake. Down-modulation of surface Mac-1 on macrophages following adherence to anti-Mac-1- or anti-CD18-coated surfaces also inhibited uptake of GBS. Further evidence for GBS interaction with CR3 was demonstrated by reduction of EC3bi rosette formation in macrophages adherent to GBS-coated plates. These studies suggest that GBS can interact with macrophage CR3, promoting phagocytosis in a C3-independent fashion. In the absence of specific immunity in neonates, this recognition mechanism may be a significant virulence determinant for GBS which poorly activate the alternate complement pathway.