Neutrophils from preterm neonates and adults show similar cell surface receptor expression: analysis using a whole blood assay.

Previous work has shown that Fc gamma RIII expression in isolated neonate neutrophils is defective. We have re-examined this phenomenon in view of the facts that (1) the receptor is present on mobilisable subcellular stores and (2) commonly used isolation procedures can affect receptor expression in suspensions of isolated neutrophils. Receptor expression was measured by fluorescence-activated cell sorter analysis of neutrophils in unfractionated whole blood. Examination of receptor expression in preterm, term and adult neutrophils indicated small but significantly decreased expression of CR1 and CR3 in preterm neutrophils compared with term neutrophils (p < 0.01). A small decrease in expression was found for Fc gamma RI and Fc gamma RIII (p < 0.05). No significant difference in expression of Fc gamma RII was observed in all groups analysed. These data suggest that isolated preterm neonate neutrophils have greatly decreased expression of Fc gamma RIII because of impaired composition or mobilisation of the subcellular stores of this receptor and/or increased lability of the surface receptor which leads to its shedding during purification.

Impaired neutrophil phagocytosis in preterm neonates: lack of correlation with expression of immunoglobulin or complement receptors.

Preterm neonates are vulnerable to infection as a result of a compromised immune system. The function of neutrophils from 'well', 'stressed', and 'maturing' preterm neonates was compared with term neonate and adult neutrophils using a whole-blood phagocytosis assay. Cell surface expression of complement receptors and immunoglobulin G receptors was measured on neutrophils in whole blood from the same samples. Fewer actively phagocytosing neutrophils were found in all preterm neonate samples, especially in maturing neonates. Phagocytic rates were slower, and the number of Escherichia coli ingested was smaller in preterm neonate than in term neonate neutrophils. Expression of immunoglobulin G receptors and complement receptor 3 on neutrophils was not directly related to phagocytic activity.

Distinct IgG1 and IgG3 subclass responses to two streptococcal protein antigens in man: analysis of antibodies to streptolysin O and M protein using standardized subclass-specific enzyme-linked immunosorbent assays.

The IgG subclass composition of antibodies to two streptococcal protein antigens in sera following infection was analysed by enzyme-linked immunosorbent assays (ELISA). The assays were standardized using 5-iodo-4-hydroxy-nitrophenacetyl (NIP)-specific chimeric antibodies, to permit quantitative comparisons between subclasses. Antibodies to streptolysin O (SLO) were predominantly IgG1, with only minor contributions from the other subclasses. In contrast, antibodies to M protein were distributed between the IgG1 and IgG3 subclasses, and in approximately half the sera IgG3 predominated. The ratio of IgG1:IgG3 was greater for SLO than for M protein in 22/23 sera. Little or no IgG4 antibody was detected to either antigen. Functional affinities of the IgG1 and IgG3 antibodies, determined by inhibition ELISA, were comparable for the two antigens. The demonstration that two protein antigens encountered during streptococcal infection elicit antibody responses with markedly different subclass profiles has implications for IgG subclass regulation and vaccine development.

Abnormal immunoglobulin G subclass production in response to keyhole limpet haemocyanin in atopic patients.

A proportion of patients with atopic dermatitis have elevated serum levels of IgG4. In order to investigate further this abnormality of IgG subclass production, atopic patients were immunized with the protein antigen keyhole limpet haemocyanin (KLH), and IgG subclass responses following primary and secondary immunization were analysed. In the primary response, titres of IgG1, 2 and 3 antibodies were lower in the atopic patients than in the controls. In contrast, titres of IgG4 were much higher for the patient group. In both patients and controls, the kinetics of IgG4 antibody production following the initial immunization with KLH showed a slow rise reaching a peak at 30 weeks. This time course indicated that the high IgG4 response was unlikely to be due to previous exposure of the patients to a cross-reacting antigen. A higher proportion of IgG4 was also seen in the atopic patients following secondary immunization; indeed, IgG4 was the major subclass in the secondary response in the patient group. In the controls, but not in the patients, titres of IgG4 anti-KLH correlated with total serum levels of IgG4, and some of the highest IgG4 antibody responses were detected in atopic patients whose serum IgG4 concentration was in the normal range. The results suggest that raised serum levels of IgG4 in atopy may reflect abnormal isotype regulation in response to protein antigens.