Damage to the immune and hematopoietic systems following exposure to i
onizing radiation, whether accidental or for therapeutic purposes, ren
ders victims susceptible to opportunistic infections and diseases. Elu
cidating a reliable biological indicator or ''biological dosimeter'' t
o indicate rapidly the extent of injury sustained by an individual wou
ld be desirable, Total leukocyte count has been used historically as a
n indicator of immune damage, but it is not truly indicative of functi
onal immunity post-irradiation. A flow cytometric (FCM) technique was
developed to determine whether a rapid reproducible assay could be dev
eloped to assess the extent of radiation damage, To this end, peripher
al blood leukocyte populations and subpopulations were monitored, C57B
L/6 mice were exposed to 100-, 400-, or 700-cGy whole-body gamma-irrad
iation (WBI) and blood samples were collected from the retro-orbital s
inus 1, 4, and 7 days post-irradiation. The blood samples were prepare
d for FCM by incubation with monoclonal antibodies (mAb) to various mu
rine leukocyte CD surface markers, The results show that the proportio
n of CD4+ T lymphocytes increased approximately 2-fold on day 4 after
700 cGy, the proportion of B lymphocytes declined markedly at all dose
s relative to unirradiated controls, and natural killer (NK) cells ros
e dramatically (9-fold) by day 4 after 700 cGy, The patterns of altera
tion in the relative proportions of peripheral blood mononuclear cells
(PBMC) populations observed post-irradiation, particularly in B lymph
ocytes and natural killer (NK) cells, seem to represent potent and con
sistent indicators of immune damage, allowing some inference as to the
immune competence of the individual. (C) 1998 Wiley-Liss, Inc.