Effect of Bronchoalveolar Lavage Fluid fromPneumocystis carinii- Infected Hosts on Phagocytic Activity of Alveolar Macrophages

Abstract

Alveolar macrophages from Pneumocystis carinii-infected rats are defective in phagocytosis. To investigate whether this defect is due to a certain factor present in P. carinii-infected lungs, alveolar macrophages from uninfected rats were incubated with bronchoalveolar lavage (BAL) fluid samples from P. carinii-infected rats. Alveolar macrophages treated with these BAL fluid samples became defective in phagocytosis but remained normal when treated with BAL fluid samples from noninfected or Toxoplasma gondii-infected rats. The suppressive activity of the BAL fluid samples from P. carinii-infected rats on phagocytosis was retained when the BAL fluid samples were passed through a filter with a pore size of 0.45 m but was lost when the BAL fluid samples were digested with proteases such as trypsin, pepsin, papain, or endopeptidase Gly-C. Lipid fractions of these BAL fluid samples had no suppressive activity on phagocytosis. The suppressive activity of these BAL fluid samples was also lost when they were incubated with concanavalin A-agarose beads, suggesting that the inhibitor is a glycoprotein. The inhibitor was estimated to be larger than 100,000 Da by exclusion filtration. After binding to the concanavalin A-agarose beads, the inhibitor in BAL fluid samples and P. carinii lysate could be eluted with 200 mM methylmannose. Treatment of both the crude BAL fluid samples and P. carinii lysate and the 200 mM methylmannose eluate with antibody against the major surface glycoprotein of P. carinii eliminated their suppressive activity. These results suggest that the factor capable of suppressing the phagocytic activity of alveolar macrophages is P. carinii major surface glycoprotein or one or more of its derivatives.An important function of alveolar macrophages is to clear foreign particles and infectious agents from the lung. Their role in the defense against Pneumocystis carinii infection is demonstrated by the observation that transtracheally inoculated P. carinii organisms are not cleared in alveolar macrophage-depleted rats (31). Administration of granulocyte-macrophage colony-stimulating factor, which activates alveolar macrophages (40), decreases the severity of P. carinii pneumonia (34). This finding also indicates the importance of alveolar macrophages in the clearance of Pneumocystis organisms.The alveoli are constantly exposed to foreign material and microorganisms. The alveolar macrophage maintains a low level of activation to engulf and destroy these materials while inhibiting an overly reactive inflammatory reaction to foreign objects encountered. To accomplish this, alveolar macrophages inhibit antigen presentation by dendritic cells (20), limit the expansion of lymphocyte populations (38), and restrict pulmonary lymphocyte functions (19). When activated, alveolar macrophages become proinflammatory and produce interleukin-8, which attracts neutrophils and lymphocytes by chemotaxis, as well as interleukin-1␤, tumor necrosis factor alpha, interleukin-6, and granulocyte-macrophage colony-stimulating factor, wh...

Suppression of Alveolar Macrophage Apoptosis Prolongs Survival of Rats and Mice withPneumocystisPneumonia

“…In this study, alveolar macrophages from Dex rats phagocytosed 21.6 Ϯ 4.2 latex beads, whereas those from Dex-Pc rats phagocytosed an average of only 1.46 Ϯ 0.2 latex beads per cell after 1 h of incubation (Fig. 6A); both results were in agreement with previous results (33). Alveolar macrophages from rats treated with caspase-9 inhibitor every 14 days beginning at the time when organisms were instilled internalized an average of 14.9 Ϯ 3.1 latex beads ( Fig.…”

“…Pneumocystis-infected L3T4-depleted mice are referred to as L3T4-depleted-Pc mice. Preparation of inoculum organisms (Pneumocystis carinii for rats and Pneumocystis murina for mice) and transtracheal inoculation were performed as described previously (33,41,43). Pneumocystis organisms from immunosuppressed and infected or just immunosuppressed animals were identified and enumerated by scoring numbers of organisms on histochemically stained impression smears from two separate lobes of lung tissue.…”

“…BAL fluids and alveolar macrophages were isolated from Normal, Dex, and Dex-Pc rats and Normal, L3T4-depleted, and L3T4-depleted-Pc mice as described previously (33,41). Animals were anesthetized with an i.m.…”

“…The importance of the alveolar macrophage in clearance of Pneumocystis organisms from the lung is ascertained by the impaired response of rats when they are depleted of macrophages (29). In immunocompromised and Pneumocystis-infected hosts, the alveolar macrophages are defective, with low levels of phagocytosis (23,(32)(33)(34) and reduced NO production (34,35). These defects are compounded by a reduction in alveolar macrophage numbers during Pcp (36 -41).…”

Polyamine-mediated Apoptosis of Alveolar Macrophages during Pneumocystis Pneumonia

“…The slow increase in organism burden in these animals agrees with previous observations in humans (53,54) and is seemingly independent of the alveolar macrophage reduction. It is possible that the organism burden is controlled by more than just the alveolar macrophage number, or that the decreased phagocytic ability (10,55) of the alveolar macrophages in Pcp renders these cells unable to control organism number even when in higher numbers.…”