Differential immune responses to albumin adducts of reactive intermediates of trichloroethene in MRL+/+ mice

Abstract

Trichloroethene (TCE) is an industrial degreasing solvent and widespread environmental contaminant. Exposure to TCE is associated with autoimmunity. The mode of action of TCE is via its oxidative metabolism, and most likely, immunotoxicity is mediated via haptenization of macromolecules and subsequent induction of immune responses. To better understand the role of protein haptenization through TCE metabolism, we immunized MRL+/+ mice with albumin adducts of various TCE reactive intermediates. Serum immunoglobulins and cytokine levels were measured to determine immune responses against haptenized albumin. We found antigen-specific IgG responses of the IgG subtypes IgG(1), IgG(2a), and IgG(2b), with IgG(1) predominating. Serum levels of G-CSF were increased in immunized mice, suggesting macrophage activation. Liver histology revealed lymphocyte infiltration in the lobules and the portal area following immunization with formyl-albumin. Our findings suggest that proteins haptenized by metabolites of TCE may act as neo-antigens that can induce humoral immune responses and T cell-mediated hepatitis.

Fig. 1

Serum concentration of albumin-specific IgG in immunized MRL +/+ mice. Control mice were injected with a mixture of PBS and adjuvant or un-adducted albumin. The immunogen (antigen used in the immunization) is indicated on the abscissa. Reactivity of immune sera (1:100 dilution) against un-adducted albumin was measured by ELISA. The data are expressed as absorbance at 450 nm. Bars represent the mean ± SEM of five mice per group tested individually. * P ≤ 0.05 compared to groups immunized with PBS or albumin.

Fig. 2

Serum concentration of immunogen-specific IgG subtypes and cross-reactivity with un-adducted albumin. Sera from mice immunized with (1) TCEO- , (2) dichloroacyl-, (3) formyl-, and (4) trifluoroacyl-albumin were tested by ELISA for IgG subtypes reactive against un-adducted albumin (black bars) and immunogen (open bars). A. Serum concentration of IgG₁ specific for albumin or the haptenized albumin used as immunogen. Sera were diluted (1:1000). B. Serum concentration of IgG_2a. Sera were diluted (1:100). C. Serum concentration of IgG_2b. Sera were diluted (1:100). Bars represent the mean ± SEM of five mice per group tested individually. * P ≤ 0.05 compared to albumin as an antigen.

Fig. 3

Liver histopathology of mice immunized with albumin (A) or formyl-albumin (B). Tissue sections were stained with H & E. Magnification 200x. The arrows in B indicate lymphocyte infiltration.