Research Articles Mechanisms of Hexachlorobenzene-Induced Adverse Immune Effects in Brown Norway Rats

Abstract

Hexachlorobenzene (HCB) is an environmental pollutant that induces adverse immune effects in humans and rats. Brown Norway rats (BN) appear to be very susceptible to HCB-induced immune effects. Oral exposure causes inflammatory skin and lung lesions, enlarged spleen and lymph nodes (LN) and elevated humoral responses. This review describes recent experiments that were performed to elucidate the mechanisms underlying these adverse immune effects. The metabolites tetrachlorohydroquinone and tetrachlorobenzoquinone are capable of generating neoantigen-specific T-cells in the mouse reporter antigen popliteal lymph node assay with 2,4,6-trinitrophenyl-Ficoll. Additional experiments in BN rats have shown that T-cells are involved in the development of HCB-induced skin lesions, the increase in auricular LN weight, lung eosinophilia, and humoral responses. However, splenomegaly and macrophage infiltration in the spleen and lung occur independent of T-cells. Remarkably, HCB does not induce T-cell sensitization in BN rats, suggesting that T-cells are activated nonspecifically, for example by macrophages. Transcriptome profiles obtained after subchronic HCB exposure to BN rats reveal that HCB induces a systemic inflammatory response in which several innate immune cells, such as macrophages, and pro-inflammatory cytokines are involved. Additional experiments have shown that macrophages are implicated in HCB-induced skin lesions, in particular in the aggravation of skin effects. Also, HCB-induced lung eosinophilia and elevation of anti-ssDNA IgM antibodies are less pronounced after macrophage elimination. Presumably, HCB activates macrophages, thereby generating pro-inflammatory adjuvant signals that induce a systemic inflammatory response. Subsequently, this may lead to polyclonal activation of T- and B-cells, eosinophilia, and eventually visible clinical effects.