Recruitment of phagocytizing cells into the respiratory tract as a response to the cytotoxic action of deposited particles.

Recruitment of phagocytizing cells into the lower respiratory tract plays a very important role in the pulmonary dust clearance, depending both on the number of particles deposited therein and on their aggressiveness. The higher cytotoxicity of the particles, the greater the number of such cells recruited and the higher the contribution of the neutrophilic leukocytes (NL) into the free cellular population of airways which normally is represented chiefly by alveolar macrophages (AM). Adaptation of the alveolar dust phagocytosis to properties of inhaled particles operates through autoregulation of this process in which a key role is played by macrophage breakdown products (PMB). A series of experiments in vitro and in vivo showed that PMB stimulate AM and NL, enhance their recruitment into airways with a dose-dependent increase of the NL/AM ratio, promote recruitment of their precursors via blood and replenishment of such precursor reserves. The most active factor of the PMB appears to be lipidic by nature. The variability between individuals and between groups of alveolar phagocytosis response to particles of a given cytotoxicity may be due to differences of the host's neurohormonal status. It was shown that influencing the latter significantly shifts response to a standard dose of the PMB.