Ds. Lang et al., LACK OF DIRECT IMMUNOSUPPRESSIVE EFFECTS OF 2,3,7,8-TETRACHLORODIBENZO-P-DIOXIN (TCDD) ON HUMAN PERIPHERAL-BLOOD LYMPHOCYTE SUBSETS IN-VITRO, Archives of toxicology, 68(5), 1994, pp. 296-302
A wide variety of immunosuppressive effects of 2,3,7,8-tetrachlorodibe
nzo-p-dioxin (TCDD) in experimental animals has been documented. In co
ntrast, the impact of dioxin on the human immune system remains contro
versial, although adverse health effects have been reported in humans
after occupational or accidental exposure to dioxin. Recently, Neubert
et al. (1991) found that a dose-dependent decrease of peripheral bloo
d lymphocyte (PBL) subpopulations in humans and nonhuman primates, inc
luding helper-inducer/memory cells (CD4(+)CD29(+)) and B cells (CD20()) occurred in pokeweed mitogen (PWM) stimulated cultures at concentra
tions as low as 10(-2)-10(-14) M TCDD. Therefore, the direct effects o
f dioxin on human PBL subpopulations have been studied, in order to de
termine their usefulness as sensitive biomarkers for human dioxin expo
sure. Lymphocyte cultures from healthy individuals were treated with 1
0(-7) M-10(-14) M TCDD in the absence and presence of stimulation with
pokeweed mitogen (PWM) or anti-CDS monoclonal antibody (moAb; OKT3) f
or 3 days. Cytochrome P450 (CYP1A1) enzyme induction, one of the best
studied direct biological study, all stimulated lymphocyte cultures sh
owed a dose-dependent significant increase of CYP1A1 activity at dioxi
n concentrations of 10(-7) and 10(-9) M. No enzyme activity could be d
etected at lower concentrations of TCDD. On the other hand, neither al
teration in surface marker distribution nor suppression of lymphocyte
proliferation could be demonstrated in mitogen-activated cells followi
ng any concentration of TCDD treatment. These data suggest that the in
ducibility of CYP1A1 enzyme activity is not correlated with direct imm
unotoxic effects in vitro in human PBL. In contrast to a previous repo
rt by Neubert et al. (1991), lymphoproliferation and phenotypes of hum
an PBL are resistant to dioxin exposure in vitro and therefore appeare
d not to be useful as sensitive biomarkers in human exposure studies.e
ffects of TCDD on numerous cell types, was assayed in parallel by etho
xyresorufin-O-deethylase (EROD) activity. Percentages of the different
lymphocytes subsets, including CD2 (T cells); CD4; CD45 RA (suppresso
r-inducer/virgin T cells); CD4 CD29; CD8; CD19 (B cells) as well as in
terleukin 2 (IL-2) receptor (CD25) and class II antigen (HLA-DR) expre
ssion, were analyzed by flow cytometry. DNA synthesis was determined b
y H-3-thymidine uptake after 3 days of culture. In the present study,
all stimulated lymphocyte cultures showed a dose-dependent significant
increase of CYP1A1 activity at dioxin concentrations of 10(-7) and 10
(-9) M. No enzyme activity could be detected at lower concentrations o
f TCDD. On the other hand, neither alteration in surface marker distri
bution nor suppression of lymphocyte proliferation could be demonstrat
ed in mitogen-activated cells following any concentration of TCDD trea
tment. These data suggest that the inducibility of CYP1A1 enzyme activ
ity is not correlated with direct immunotoxic effects in vitro in huma
n PBL. In contrast to a previous report by Neubert et al. (1991), lymp
hoproliferation and phenotypes of human PBL are resistant to dioxin ex
posure in vitro and therefore appeared not to be useful as sensitive b
iomarkers in human exposure studies.