REDUCED CD4 AND HLA-DR EXPRESSION IN NEONATAL MONOCYTES

Three-color flow cytometry was used to assess the immunophenotypic cha racteristics of normal cord blood monocytes after labeling with a vari ety of antibodies against myeloid/monocyte-specific markers. Monocytes both in cord blood and in peripheral blood from normal adults were de fined in a backgating procedure as cells with the light-scattering cha racteristics of monocytes that also expressed CD14. The percentage of monocytes, defined in this fashion, that also displayed CD4 receptors was significantly lower in cord blood (mean +/- SD = 29.3 +/- 13.9%) t han in peripheral blood from normal adult controls (mean +/- SD = 68.9 +/- 13%) (P < 0.005). Similarly, HLA-DR expression was found on only 86 +/- 6.6% of monocytes in cord blood but on 99 +/- 1% of monocytes i n adults (P < 0.005), The percentage of monocytes displaying CD16 rece ptors in cord blood did not show any significant difference in compari son with adult monocytes. When coexpression of CD14, CD16, and CD4 was assessed, cord blood showed a predominant population of monocytes bea ring the phenotype CD14+/CD16-/CD4-. Similarly, approximately 10% of C D14+ monocytes in cord blood expressed neither CD4 nor HLA-DR. Cytoche mically, monocytes from cord blood revealed intense granular staining for PAS and marginal or absent staining for nonspecific esterase (NSE) . These results raise the possibility that reduced expression of CD4 a nd HLA-DR receptors on cord blood monocytes may contribute to their im paired immune response. Additionally, the high percentage of CD14+/CD1 6-/CD4- cells in cord blood suggests that these cells may represent a phenotypically immature population of monocytes. Likewise, the unusual cytochemical staining patterns suggest that these cells are biochemic ally immature as well. (C) 1998 Academic Press.