Aldicarb treatment inhibits the stimulatory activity of macrophages without affecting the T-cell responses in the syngeneic mixed lymphocyte reaction

Pesticides and other agricultural factors associated with self-reported farmer's lung among farm residents in the Agricultural Health Study

BACKGROUND

Farmer's lung, or hypersensitivity pneumonitis, is an important contributor to respiratory morbidity among farmers.

METHODS

Using the 1993-7 enrolment data from the Agricultural Health Study, we conducted a cross-sectional study of occupational risk factors for farmer's lung among 50,000 farmers and farm spouses in Iowa and North Carolina using hierarchical logistic regression controlling for age, state, and smoking status. Participants provided information on agricultural exposures, demographic characteristics, and medical history via self-administered questionnaires. Approximately 2% of farmers (n = 481) and 0.2% of spouses (n = 51) reported doctor-diagnosed farmer's lung during their lifetime. We assessed farmers and spouses separately due to different information on occupational exposure history. Only pesticide exposures represented lifetime exposure history, all other farm exposures represented current activities at enrolment.

RESULTS

Among farmers, handling silage (OR = 1.41, 95% CI 1.10 to 1.82), high pesticide exposure events (OR = 1.75, 95% CI 1.39 to 2.21), and ever use of organochlorine (OR = 1.34, 95% CI 1.04 to 1.74) and carbamate pesticides (OR = 1.32, 95% CI 1.03 to 1.68) were associated with farmer's lung in mutually-adjusted models. The insecticides DDT, lindane, and aldicarb were positively associated with farmer's lung among farmers. Current animal exposures, while not statistically significant, were positively associated with farmer's lung, particularly for poultry houses (OR = 1.55, 95% CI 0.93 to 2.58) and dairy cattle (OR = 1.28, 95% CI 0.86 to 1.89). The occupational data were more limited for spouses; however, we saw similar associations for dairy cattle (OR = 1.50, 95% CI 0.72 to 3.14) and organochlorine pesticides (OR = 1.29, 95% CI 0.64 to 2.59).

CONCLUSION

While historic farm exposures may contribute to the observed associations with pesticides, these results suggest that organochlorine and carbamate pesticides should be further evaluated as potential risk factors for farmer's lung

Effects of pesticide exposure on serum immunoglobulin and complement levels

Serum immunoglobulins (IgG, IgA and IgM), C3 and C4 complement protein levels were examined in the male workers of the municipality who routinely applied pesticides for at least one year, and compared to healthy male controls in order to determine whether immune alterations were evident in the pesticide-exposed workers. Pyrethroids were the most commonly used pesticides for the last 3 years. Serum immunoglobulins and complement levels were measured by turbidimetry. Serum IgG, IgA, IgM and C3 complement levels were found to be unchanged when compared to controls whereas a significant decrease was observed in serum C4 complement levels of the workers.

Carbofuran suppresses T-cell-mediated immune responses by the suppression of T-cell responsiveness, the differential inhibition of cytokine production, and NO production in macrophages

The effects of carbofuran (2,3-dihydro-2,2-dimethyl-7-benzo-furanol N-methylcarbamate) on the functions of T cells in splenocytes and peritoneal macrophages were examined in view of T-cell-mediated immune response (CMIR) in male C57BL/6 mice. Intraperitoneal administration of carbofuran (0.075, 0.15 and 0.3 mg/kg body weight) resulted in significant suppression of delayed type hypersensitivity (DTH), indicating that it caused the suppression of CMIR. Carbofuran decreased Concanavalin A (Con A)- and alloantigen-induced proliferation, and interleukin (IL)-2 production of splenocytes. In vitro addition of rIL-2 could not completely restore the suppressed T-cell proliferation, and IL-2-induced proliferation of Con A-activated splenocytes was also suppressed, which implied that carbofuran caused defects in IL-2 production and responsiveness of splenocytes to IL-2, leading to the suppression of T-cell proliferation. Con A-induced production of interferon-gamma (IFN-gamma) was significantly suppressed by carbofuran, while that of IL-4 was not affected. The production of transforming growth factor-beta from splenocytes was also significantly inhibited by carbofuran. Judging from these results, carbofuran might directly suppress the cytokine production in T helper 1 (Th1) cells. In addition, IFN-gamma-induced production of nitric oxide (NO) in macrophages was also inhibited by carbofuran, which might be one of the important mechanisms of carbofuran-induced CMIR suppression in mice. Collectively, the present study suggests that carbofuran might suppress CMIR through the suppression of T-cell responsiveness, IFN-gamma production in Th1 cells, and NO generation in macrophages.

Immunotoxicity of pesticides: a review

The intricate balance that is the hallmark of the immune system shows vulnerability to any chemical, including pesticides, that can cause structural and functional alterations to the system. The immunotoxic effects of xenobiotics include: histopathologic effects in immune tissues and organs; cellular pathology; altered maturation of immunocompetent cells; changes in B and T cell subpopulations; and functional alterations of immunocompetent cells. Pesticides, including fungicides, herbicides, and insecticides, are the only class of chemicals deliberately released into the environment because of their toxicity. Around the world, millions of people are exposed to pesticides at work and/or in their home. This article reviews evidence, from animal and human studies, on the effects of pesticides on the immune system.

Immunotoxicity of subchronic versus chronic exposure to aldicarb in mice

In this study we compared the immunotoxicity of subchronic vs chronic exposure to the aldicarb insecticide at a relatively low, 0.1-10 ppb, level in drinking water. The immunotoxicity of aldicarb was evaluated in 28- and 90-day studies by determination of the humoral, cellular and nonspecific immunity in inbred C57BL/6 mice. Quantification of splenic plaque-forming cells (PFC) to sheep erythrocytes (SRBC), mitogen activation of spleen lymphocytes, mixed lymphocyte reaction (MLR) and the cytofluorometric assay of the phagocytic uptake of fluorescent beads were among the parameters studied. Neither the cell viability nor the splenic cell count was affected by the insecticide exposure. Immunophenotyping and cytometric determination of L3T4+, Lyt2+ and Ig+ cells revealed no effect of the insecticide exposure on the total count of cell subsets in the ungated splenocyte population. However, a marked shift in the percentages of L3T4+ and Lyt2+ cells was noted after subchronic exposure to 1 and 10 ppb aldicarb, possibly indicating activation of these splenic T-cell subsets. Subchronic aldicarb exposure significantly suppressed the splenic PFC response to SRBC at 1 ppb dose, however, no dose-effect correlation could be concluded. Similarly, no dose-effect correlation was observed for subchronic aldicarb-related changes in mitogen responses. Subchronic exposure to aldicarb had no statistically significant effect on the mixed lymphocyte reaction (MLR) or on the macrophage phagocytosis. Chronic exposure to 0.1-10 ppb aldicarb did not affect any of the parameters measured, including the cell subsets. Thus, aldicarb-related changes in immune parameters, noted after a 28-day exposure, were compensated over chronic exposure to the insecticide.

Immunosuppression by aldicarb of T cell responses to antigen-specific and polyclonal stimuli results from defective IL-1 production by the macrophages

In the present study we investigated the immunomodulatory effects of aldicarb, a carbamate pesticide, on T cells activated by a number of different ways. When C3H mice were injected intraperitoneally with a single dose of Aldicarb, 0.005-50 micrograms/kg body wt, and their spleen cells were stimulated with T cell mitogens such as concanavalin A (ConA)3 or anti-CD3 monoclonal antibodies (mAb), a decreased responsiveness was detected when compared to the control mice. Aldicarb administered at concentrations less than 0.005 microgram/kg body wt failed to cause significant immunosuppression. Interestingly, when purified T cells from immunosuppressive doses of aldicarb-treated mice were stimulated with ConA in the presence of irradiated control macrophages, the defective T cell response was no longer demonstrable. Also, purified control T cells stimulated with ConA in the presence of irradiated macrophages from aldicarb-treated mice showed decreased responsiveness. Similar observations were made using anti-CD3 mAb to activate the T cells, inasmuch as whole spleen cells from aldicarb-treated mice showed decreased responsiveness to anti-CD3 stimulation, whereas purified T cells in the presence of irradiated control macrophages showed normal reactivity. The fact that aldicarb did not directly affect the T cell functions was further confirmed by stimulating purified T cells from aldicarb-treated mice with phorbol myristate acetate and calcium ionophore, a response which is independent of the accessory cells and which was found to be normal in aldicarb-treated mice. It was observed that the macrophages from aldicarb-treated mice demonstrated a decreased capacity to stimulate conalbumin-specific T helper cell clone, D10.G4, and when activated produced decreased amounts of IL-1 when compared to control macrophages. Also, the decreased stimulation of D10.G4 clone by aldicarb-treated macrophages was reconstituted when exogenous recombinant IL-1 was added to the cultures. These data together suggested that aldicarb affects the macrophage functions by interfering with IL-1 production and that it does not affect the T cell functions directly.

Immunomodulatory effects of nitrosoureas on the phenotype and functions of T cells in the thymus and periphery

We have recently demonstrated that nitrosoureas such as 1,3-bis-(2-chloroethyl)-1-nitrosourea (BCNU) and chlorozotocin (CLZ) can cure almost 100% of mice bearing LSA tumor, syngeneic to C57BL/6 mice. In contrast, similar or higher doses of streptozotocin (STZ) completely failed to cure LSA-bearing mice. Further studies revealed that the efficacy of nitrosoureas may depend on their immunomodulating properties. In the current study, therefore, we investigated the effect of these nitrosoureas on the immune system of normal mice. Treatment of C57BL/6 mice with 5 intraperitoneal injections of 20 mg/kg body weight of BCNU or CLZ caused an increase in the percentage of CD4(-)CD8- T cells and a decrease in the percentage of CD4(+)CD8+ T cells in the thymus. In addition, such treatment also caused an increase in the percentage of CD4+ T cells without significantly affecting the CD8+ T cells in the thymus. However, when total cellularity of the thymus was studied, BCNU and CLZ were found to decrease the total number of CD4(+)CD8+ T cells without significantly affecting the other subsets. In contrast, similar or higher (100 mg/kg body weight) doses of STZ had no significant effect on the total number and percentages of T cell subsets in the thymus. Also BCNU and CLZ but not STZ treatment caused a 50% decrease in the total number of CD4+ and CD8+ T cells in the spleen. When T cells in the spleens of nitrosourea-treated mice were functionally analysed, it was observed that BCNU and CLZ caused a dramatic decrease in the T cell responsiveness to ConA, anti-CD3 and phorbol myristate acetate plus calcium ionophore stimulation. In contrast, STZ treatment failed to significantly inhibit the T cell responsiveness to these activation signals. Using the accessory cell-dependent and -independent assays, BCNU and CLZ were found to suppress the functions of both T cells and macrophages. Also, addition of growth factors such as IL-1, IL-2, IL-4 and IL-6 failed to reconstitute the defective responsiveness of BCNU- and CLZ-treated T cells and macrophages. Together our data suggest that nitrosoureas have varying immunomodulating properties and this may in turn determine their efficacy in the treatment of cancer.