Flow cytometry was used to assess CD4 expression in 62 consecutive bon
e marrow specimens from patients with a variety of clinical conditions
. Using a lysed-whole-blood technique for labeling with monoclonal ant
ibodies, two populations of CD4(+) cells were identified within the ly
mphocyte/blast-cell fraction in 58 (94%) of these specimens. These con
sisted of (1) a population of T helper cells with high-density express
ion of CD4 and (2) a second population of cells with low-density expre
ssion of CD4. which ranged from 1% to 36% of the gated cells. This lat
ter population was present regardless of age. sex. or clinical conditi
on including 21 of 21 specimens (100%) categorized as unremarkable bon
e marrows both morphologically and by flow cytometry and in four of fo
ur patients (100%) with human immunodeficiency virus-type 1 (HIV-1) in
fection. Coexpression of the erythroid lineage marker, glycophorin A,
with the majority of cells in this second population was demonstrated
in all 11 randomly selected samples using two-color flow cytometric an
alysis. These cells also expressed low levels of the myeloid markers.
CD13 and CD33. but CD34 expression could not be demonstrated. These re
sults provide evidence for expression of CD4 on cells of erythroid lin
eage in human bone marrow, and offer a potential mechanism for direct
infection of erythroid precursor cells and deranged erythropoiesis in
patients with HIV-1 infection. (C) 1996 by The American Society of Hem
atology.