3-Methylcholanthrene induces differential inhibition of humoral and cell mediated immune responses in mice of different ages

Methylcholanthrene causes increased thymocyte apoptosis

The polycyclic aromatic hydrocarbon (PAH), methylcholanthrene (MCA), is a well studied carcinogen and a teratogen. MCA and other PAH cause immune suppression of B cell and T cell responses in mice and MCA had been reported to induce thymus atrophy. Here we show that MCA treatment causes thymus atrophy in adrenalectomized mice and in C57BL/6 and DBA/2 mice which differ in aryl hydrocarbon receptor (AhR) expression. This indicates that MCA-mediated thymus atrophy is mediated, at least in part, by glucocorticoid hormone receptor- and aryl hydrocarbon receptor-independent mechanisms. Assay of thymocytes, both in situ and ex vivo, demonstrate that MCA induces thymocyte apoptosis. Apoptotic thymocytes can be found within or adjacent to thymic Mphi, suggesting rapid phagocytosis. Mice that are deficient in tumor necrosis factor-alpha receptor-1 or p53, or that overexpress bcl-2 are susceptible to MCA-mediated thymus atrophy.

Immunotoxicity of a reconstituted polynuclear aromatic hydrocarbon mixture in B6C3F1 mice

Previous studies on the immunotoxicity of a complex mixture of polynuclear aromatic hydrocarbon (PAH) by-products from a manufactured gas plant indicated possible synergistic interactions which were investigated by determining the immunosuppressive effects of a reconstituted PAH mixture in female B6C3F1 mice challenged with TNP-haptenated sheep red blood cells (SRBCs) (T-cell-dependent) or trinitrophenyl-lipopolysaccharide (TNP-LPS) (T-cell-independent) antigens. The reconstituted PAH mixture contained the following 17 congeners: 2-rings (indan, naphthalene, 1- and 2-methylnaphthalene), 3-rings (acenaphthylene, acenaphthene, dibenzofuran, fluorene, phenanthrene and anthracene), and > or = 4-rings (pyrene, fluoranthene, benz[a]anthracene, chrysene, benzo[b]fluoranthene, benzo[k]fluoranthene and benzo[a]pyrene), and resembled mixtures identified as by-products from manufactured gas plants. The reconstituted mixture and the 2-, 3- and > or = 4-ring PAH fractions all caused a dose-dependent decrease in the splenic plaque-forming cell (PFC) response to SRBCs or TNP-LPS, and their ED50 values for the four treatment groups were 86, 354, 145, and 23 or 163, 439, 637 and 31 mg/kg, respectively. The corresponding ED50 values for decreased serum anti-TNP IgM levels for these same mixtures were (TNP-haptenated SRBCs, T-cell-dependent) 144, 231, 42 and 27 units, respectively, and (TNP-LPS, T-cell-independent) 161, 406, 312 and 69 units, respectively. The suppression of anti-TNP IgM titers was similar to the suppression of the PFC response and shows that antigen-specific immunoglobulin titer can be used as a biomarker of PAH exposure. A direct comparison of the immunotoxic responses of the reconstituted PAH mixture and the corresponding dose of the > or = 4-ring PAHs indicated that the latter fraction was primarily responsible for the activity of the reconstituted mixture.

Characterization of a chemically induced tumor model and the effects of natural killer cell depletion by antiasialo GM-1

A tumor model in the Sprague-Dawley rat has been developed and characterized in our laboratory using the polycyclic aromatic hydrocarbon 3-methylcholanthrene (3MC). Interactions between the tumorigenic process and the natural killer cell (NK) response were investigated in this study. Rats given a single injection of 1.5 mg 3MC had reduced NK activity the first three weeks after injection when compared to vehicle treated controls. Tumor incidence in this group reached 45% and 76% 12 and 20 weeks, respectively, after the 3MC injection. Cell lines were established from six of these tumors and were tested for in vitro lysis by NK cells. Sensitivity of these cells ranged from 2.9 to 12.2% compared to 32.3 to 37.5% for the NK sensitive YAC-1 target cells. Rabbit antiasialo GM-1 antibody (ASGM-1) was used to effect in vivo reductions of NK function at arbitrarily selected times after 3MC injection. Tumor incidence in the group of rats treated to reduce NK activity at the time of initiation (0-2 weeks) reached 100% in 20 weeks compared to 67% in the companion 3MC treated controls. The number of days to tumor was also decreased from 93 to 77 days in this group. Rats treated to reduce NK activity at other times (5-7 weeks or 10-12 weeks) did not have alterations in tumor incidence or latency that were different from controls. The study supports a role for NK cells in the early detection and removal of transformed cells and points out the dangers of transient immunosuppression.

The unique interaction with immunity of FCE 24517, an antitumor drug with a novel mode of action

The present study was designed to characterize in mice the effects on the immune system of the antineoplastic agent FCE 24517, a benzoic acid mustard derivative of distamycin A with specificity for AT-rich base pair sequences of beta-DNA. At antitumorally therapeutic doses, single injections of FCE 24517 caused profound leukopenia and a decrease of spleen cell numbers. However, primary and secondary antibody production to the T-dependent antigen sheep red blood cells were markedly increased by FCE 24517 given before or together with antigen. Antibody production to the T-independent antigen type III pneumococcal polysaccharide was not appreciably affected by FCE 24517. The delayed type hypersensitivity response to sheep erythrocytes was only marginally decreased, whereas proliferation of spleen cells to mitogens was markedly depressed. The ability of natural killer cells and macrophages to mediate cytotoxicity was not affected by FCE 24517 treatment. The ability of carrier-primed cells from drug-treated mice to cooperate for anti-trinitrophenyl antibody production increased twofold over that of vehicle-injected controls, suggesting an increase in T-helper cell activity. Serum cytokine levels were studied in mice injected with bacterial lipopolysaccharide used as a model stimulus. Peak levels of TNF and IL-6 were not modified by FCE 24517, but at later times higher amounts of cytokines were found in drug-treated mice compared with the control, suggesting a longer exposure of immunocompetent cells to these factors. Two compounds (FCE 24561 and CC-1065), also capable of binding AT-rich sequences in the minor groove of beta-DNA and containing an alkylating moiety, had immunomodulatory activity similar to FCE 24517 in increasing primary anti-sheep erythrocytes response. It is concluded that FCE 24517 exhibits a unique interaction with the immune system, markedly different from that of alkylating agents and may be representative of a novel group of antiproliferative-immunomodulating agents.