Inhalation studies of Mt. St. Helens volcanic ash in animals. III. Host defense mechanisms.

The effects of inhalation exposure of mice or rats to 9.4 mg/m3 volcanic ash, 2.5 mg/m3 SO2, or both on host defense mechanisms were assessed. Cytologic changes in pulmonary lavage fluid included an increase in percentage polymorphonuclear leukocytes due to SO2 exposure and an increase in eosinophils due to ash. SO2 and ash also produced decreases in percentage alveolar macrophages. In the case of ash-exposed animals, this decrease was offset by an increase in lymphocytes. Total cell counts and viability were not affected by any of the exposures. Pulmonary clearance mechanisms were affected in that there were both decreased alveolar macrophage phagocytic capability following ash and ash + SO2 exposures and depressed ciliary beat frequency attributable to ash exposure. None of the inhalation exposures caused increases in susceptibility to an immediate or 24 hr postexposure aerosol challenge with Streptococcus. However, intratracheal instillation of both fine- and coarse-mode volcanic ash caused slight but significant increases in mortality due to bacterial challenge 24 hr after the instillation. The phytohemagglutinin-induced blastogenic response of splenic lymphocytes from exposed animals did not differ significantly from that of control lymphocytes, although the lipopolysaccharide-induced blastogenic response was enhanced. Ash exposure had no effect on susceptibility to murine cytomegalovirus. In summary, volcanic ash alone or in combination with SO2 had only minimal effects on certain host defense mechanisms.