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.