Relative leucopenia in the peripheral blood of asbestos miners: a epidemiologic analysis

Suppression of the in vitro humoral immune response by chrysotile asbestos

The direct addition of UICC chrysotile B asbestos to spleen cell cultures produced a dose-dependent suppression of the antibody-forming cell (AFC) response to the T-dependent antigen, sheep erythrocytes. Concentrations of 0.1, 1, 10, and 100 micrograms/ml, which had no effect on either cell number or viability, suppressed the in vitro response by 12, 43, 71, and 95%, respectively. By separating spleen cells into nonadherent and plastic-adherent populations, the effects of asbestos on each cell type were studied utilizing reconstituted cultures. Treatment of adherent cells for 1 hr with asbestos and reconstitution with untreated nonadherent cells resulted in a dose-dependent suppression of the AFC response similar to that observed when asbestos was added to whole spleen cultures. Reconstitution studies were also conducted with spleen cell populations from animals administered asbestos in vivo. In cultures reconstituted with adherent cells from asbestos-treated mice and nonadherent cells from saline-treated animals, the AFC response was significantly suppressed. The T-dependent AFC response with reconstitution of adherent cells from saline-treated mice and nonadherent cells from asbestos-exposed animals was no different from reconstituted saline controls. Both adherent alveolar and pleural cells were capable of reconstituting the T-dependent AFC response with nonadherent spleen cells and demonstrated reduced immunological capability when exposed to asbestos fibers. The results of this investigation have identified the adherent spleen cell (macrophage) as the target cell type responsible for asbestos-induced immunosuppression of the in vitro T-dependent antibody-forming cell response.

Bone marrow alterations induced in mice with inhalation of chrysotile asbestos

The effect of chrysotile asbestos exposure on bone marrow and immune parameters was examined in mice at 2, 12, and 26 weeks following a 3-day inhalation exposure. Ultrastructural examination revealed that the fibers were deposited primarily at alveolar duct bifurcations within the centriacinar region of the lung. Histological pulmonary changes were minimal, but by 26 weeks early asbestosis characterized by clusters of macrophages and minimal fibrosis were present in the centriacinar region of the lung. Lymphoproliferative responses, antibody levels, and number of plaque forming cells were not significantly altered in exposed mice. Pulmonary macrophages, but not peritoneal macrophages, showed evidence of activation in the chrysotile-exposed mice at 26 weeks following exposure. The most striking change was the depression of the number of bone marrow pluripotent stem cells (CFU-S) and marrow granulocyte macrophage progenitors (CFU-GM) which were lower at all three postexposure examinations. It is felt that the depression of bone marrow progenitors in asbestos-exposed mice may have relevance to the leukopenia reported in workers with occupational history of asbestos exposure.

Asbestos as a systemic carcinogen: the evidence from eleven cohorts

Most known occupational carcinogens are site-specific, which implies that they are "complete" carcinogens with both "initiating" and "promoting" properties (Berenblum's terminology). Excess cancer at gastrointestinal sites among cohorts occupationally exposed to asbestos has been interpreted as reflecting additional site-specific effects, although excess at other sites has also been observed in some studies. The hypothesis that excess cancer at gastrointestinal sites cannot be distinguished from excess cancer at all nonpulmonary sites is tested by data from New York-New Jersey insulation workers working in 1943; similar workers employed after 1943; U.S.-Canadian insulation workers; London factory workers, male and female; Quebec miners and millers; retired U.S. factory workers; U.S. shipyard insulators; Italian shipyard workers in Genoa; Amosite factory workers; and U.S. factory workers. Excluding lung cancer and mesothelioma, observed-expected ratios for nonpulmonary cancer mortality range from 0.97 to 2.78, and do not differ significantly from gastrointestinal ratios. A dose-response gradient is observed for both ratios, when dose is estimated from lung cancer ratios, or in some studies, measured exposures. Site-specificity is unlikely for nonpulmonary cancer associated with asbestos exposure more than 20 years previously. Systemic carcinogenesis may be an example of promotion or impairment by asbestos of some cancer defense mechanism; immunological mechanisms have been suggested by Turner-Warwick and Parkes. Prospective studies are indicated.