Characterization of Basophils in Infants in the Microbes, Allergy, Asthma and Pets (MAAP) Birth Cohort

Basophils are mature circulating granulocytic cells that play an important role in IgE-dependent immune responses. The objective of this study was to prospectively examine, in very early life, basophils for FcεRIα and activation markers, which are involved in a Th2 response. Cord blood and venous blood at 6 months of age were obtained from 65 infants enrolled in the MAAP (Microbes, Allergy, Asthma and Pets) birth cohort. Basophil percentages were determined by manual differential count of 200 cells in whole blood smears. The enriched granulocyte fraction collected after Ficoll separation of peripheral blood mononuclear cells was examined by flow cytometry. Basophils were defined as low side scatter/Class II −/CD123+ cells. Cells expressing FcεRIα or the activation markers CD203c or CD63 were examined and were reported as % of basophils expressing these markers. Paired t-tests were used to assess change over time. Basophils represented a mean 0.78% (range 0 to 2.5%) and 0.88% (range 0 to 4.0%) of the differential among cord and 6 month blood samples, respectively. There was a statistically significant increase from birth to 6 months of age in the proportion of basophils expressing FcεRIα (mean increase 12.7%, p=0.007), CD203c (mean increase 16.7%, p<0.001) or CD63 (mean increase 20.3%, p<0.001). The longitudinal investigation of basophils in samples from the first months of life makes this study distinctive. The increase in the proportion of basophils that were either CD203c+, CD63+, or FcεRIα+ suggests the rapid development of this aspect of innate immunity during the earliest prenatal period.