INTRATRACHEAL INSTILLATION VERSUS INTRATRACHEAL INHALATION - INFLUENCE OF CYTOKINES ON INFLAMMATORY RESPONSE

Our laboratory has developed a method of particle exposure whereby ane sthetized rats intratracheally inhale, at a regulated breathing rate a nd pressure, an aerosolized test material. This method is capable of d elivering considerable doses in a short time period and, unlike the co mmonly used method of intratracheal instillation, does so with an even particle distribution throughout the lung. Early studies comparing th e response of mall Fischer 344 rats exposed to TiO2 particles of two d iffering primary particle sizes showed that at similar particle doses animals exposed by the two methods showed differences in response, as measured by bronchoalveolar lavage (BAL) parameters. Building on this, we sought to study the roles that macrophage inflammatory protein-2 ( MIP-2) and tumor necrosis factor alpha (TNF-alpha), two cytokines thou ght to have proinflammatory roles in the lung, may play in the differe nces observed. Increases in MIP-2 protein levels in the lavaged cells, but not the supernatant, were observed in those groups where increase d polymorphonuclear cells (PMN) in the lung lavage were found, but not in those where no increase in PMN levels was observed. BAL TNF-alpha levels, measured by enzyme-linked immunosorbent assay, showed no appar ent correlation with cellular or biochemical BAL parameters for either particle size or dosing method. increases in immunocytochemical stain ing for TNF-alpha, compared to unexposed controls, were observed in se veral particle-exposed groups. Thus, it appears that increased BAL MIP -2 protein levels, but not TNF-alpha, correlate well with the inflamma tory response, as measured by PMN numbers in lavaged cells, for both e xposure systems.