Role of RT6⁺T lymphocytes in mercury‐induced renal autoimmunity: Experimental manipulations of “susceptible” and “resistant” rats

Abstract

Brown Norway (BN) rats, "susceptible" to the autoimmune effects of mercury, experience a decrease of peripheral RT6.2+ T lymphocytes after the injection of relatively low doses of mercuric chloride. This change coincides with the appearance of circulating autoantibodies to renal antigens (e.g., laminin). Lewis (LEW) rats, "resistant" to the autoimmune effects of mercury, do not show significant decreases of RT6+ T cells. It is possible that BN rats are particularly sensitive to stress induced by mercury and that secretion of adrenocortical hormones decreases levels of RT6+ T cells in this rat strain. Alternatively, mercury may induce a graft-versus-host-like syndrome in BN rats, resulting in higher levels of corticosteroids capable of affecting RT6+ lymphocytes. To eliminate the possible influence of adrenocortical hormones, we have adrenalectomized BN rats prior to administration of mercury. Autoimmune responses to renal antigens were not affected by this experimental manipulation. Similarly, adrenalectomized rats exposed to mercury showed a significant decrease of RT6+ T lymphocytes in cervical lymph nodes. Overall, these observations do not support the hypothesis that increases in adrenocortical hormones play a major role in mercury-induced changes of RT6+ T cells. We have also explored whether experimental depletion of RT6+ T lymphocytes would result in autoimmunity. Gamma irradiation of BN rats led to a decrease of RT6+ T splenocytes, but by itself (i.e., without exposure to mercury) did not cause autoimmune responses to renal antigens. In addition, gamma-irradiated BN rats treated with mercury had autoimmune responses similar to those observed in mercury-treated nonirradiated controls. Depletion of RT6+ T cells in LEW rats through the use of a monoclonal antibody against the RT6.1 alloantigen did not by itself cause renal autoimmunity in this "resistant" strain. Depletion followed by administration of mercury also failed to induce renal autoimmunity. The lack of autoimmune effects in RT6-depleted BN and LEW rats suggests that a combination of several factors may be necessary to break self-tolerance and cause mercury-induced autoimmunity. Such factors likely comprise both environmental (mercury) and endogenous, genetically determined components. The latter include regulatory T cells (possibly RT6+), major histocompatibility complex (MHC), and T-cell receptors (TCR). Thus, BN rats with decreased percentages of immunoregulatory RT6+ T lymphocytes require additional immunotoxic and/or toxic effects of mercury for autoimmunity to occur. On the other hand, LEW rats depleted of regulatory T cells may still be unable to develop renal autoimmunity after exposure to mercury because they lack the appropriate MHC and TCR.

Toxicology and Immunotoxicology of Mercury: A Comparative Review in Fish and Humans

“…In rodents, HgCl 2 modulates T cells by induction of interleukins (IL) (e.g., IL-1 b ) and immunoglobulins (Ig) (e.g., IgG and IgE) (Griem et al, 1998), and by altering expression of costimulatory molecules (Roos et al, 1996); Hg stimulation of B lymphocytes may also mediate autoimmunity (Druet et al, 1982;Rose, 1993). In rodents, other features of Hg-induced autoimmune disease include generation of autoreactive CD4 + T cells (inhibition of Th1 and enhancement of Th2 subsets); synthesis of autoantibodies; glomerulonephritis; hypergammaglobulinemia; and regulation by IL-2 (Lawrence & McCabe, 1995;Kosuda et al, 1994Kosuda et al, , 1998Jiang & Moller, 1999;Abedi-Valugerdi et al, 1999). Interestingly, significant induction of serum concentrations of IgA, IgG, and IgM (compared to nonexposed healthy subjects) was observed in human workers exposed to Hg occupationally .…”

“…Moreover, there is evidence that gender differences (via different endogenous levels of sulfhydryl groups) may be another factor affecting the apparent enhanced susceptibility of males to Hg toxicity (Calabrese, 1985). These age-and gender-dependent differences may point to select populations being more susceptible to toxicantinduced immunomodulation (Kosuda et al, 1994;Barnett, 1997).…”

NAD+-dependent ADP-ribosylation of T Lymphocyte Alloantigen RT6.1 Reversibly Proceeding in Intact Rat Lymphocytes

“…Although the physiological role of RT6 in a specific cell function is still unknown, its defect in lymphocytes has been implicated in disorders of diabetes and mercury-induced renal autoimmunity in animal models (12)(13)(14). Recent biochemical analysis reveals that there are at least two types of RT6 alloantigen, RT6.1 and RT6.2, and both are covalently anchored in cell surface membranes via GPI linkage (15,16).…”

Gestational exposure to mercury leads to persistent changes in T-cell phenotype and function in adult DBF1mice

“…Further, emerging data chiefly from the work of Kosuda and co-workers (Kosuda et al, 1991) have given support for modulations in T reg function in the pathogenesis of metal-induced autoimmune diseases. In susceptible Brown-Norway (BN) rats treated with mercury, depletion of immunoregulatory RT6 + T-lymphocytes was found to coincide with the appearance of autoantibodies in the serum and immune complex glomerulonephritis (Kosuda et al, 1991(Kosuda et al, , 1993(Kosuda et al, , 1994(Kosuda et al, , 1998. Further, in H-2 S mice, the adoptive transfer of CD4 + CD25…”