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The processes of phagocytosis and intracellular killing of bacteria by alveolar macrophages (AMs) and polymorphonuclear leukocytes (PMNs) result in the production of reactive oxygen species that can induce self-damage to the phagocytic cells. N-Acetylcysteine (NAC), a mucolytic agent used to treat chronic respiratory inflammatory disorders, possesses antioxidant properties and has therefore been used for the prevention of damage induced by oxygen radicals. This study was designed to evaluate whether NAC can interfere with the processes of phagocytosis and intracellular killing of bacteria and protect the phagocytic cells from self-killing. Human AM, obtained by bronchoalveolar lavage, and peripheral blood PMNs were cultured with Staphylococcus aureus (American Type Culture Collection 25923 strain) in the presence of different concentrations of NAC (1, 10, and 100 mg/L) and two chromophores (4',6'-diamidino-2-phenylindole dihydrochloride and propidium iodide), which identify live or dead bacteria and dead phagocytes. As compared with PMNs, AMs were more effective in ingesting bacteria (p0.05) and were equally effective as intracellular killers (p0.05), but were susceptible to a significantly higher rate of self-killing (p0.01). The presence of NAC in the cell cultures at the highest dose tested (100 mg/L) induced a significant enhancement of the bactericidal activity of both AMs (p0.05) and PMNs (p0.05). This increased intracellular killing was not associated with increased proportions of dead phagocytes either in AMs or PMNs cultures (p0.05, each comparison), suggesting a protective effect of NAC on damage induced by toxic products generated during phagocytosis.

Thymomodulin (TMD), a thymic biological response modifier, stimulates the release of tumour necrosis factor (TNF) and granulocyte-macrophage-colony stimulating factor (GM-CSF) in macrophage-lymphocyte cultures. We investigated the effects of the cytokines released in cultures with TMD, on the expression of human leucocyte antigen-DR (HLA-DR) antigens by alveolar macrophages (AM) and the T-cell proliferation induced in autologous mixed leucocyte reaction (AMLR) cultures or by T-cell mitogens. Among freshly isolated AM, 84 +/- 4% were HLA-DR positive, and this proportion was significantly reduced after 24 h cultures (60 +/- 3%, p < 0.05). In cultures without peripheral blood (PBL) lymphocytes, TMD did not change HLA-DR expression by AM CHLA-DR+AM); whilst in the presence of autologous PBL lymphocytes, TMD induced an increase in the proportions of HLA-DR+AM (TMD 100 micrograms.ml-1 79 + 3%, p < 0.04 vs control cultures). However, TMD did not change the ability of AM to induce T-cell proliferation in AMLR between AM and PBL lymphocytes. In contrast, in PBL mononuclear cell cultures, TMD induced a further increase of the cell proliferation due to the T-cell mitogens interleukin-2 (IL-2) or phytohaemagglutinin (PHA) (p < 0.05 vs each control culture with mitogens) or anti-CD3 antibodies (p < 0.03 vs control cultures). Thus, the cytokines released in cultures with TMD enhance macrophage HLA-DR expression. Whilst this phenomenon is not associated with changes in the ability of AM to stimulate T-cell proliferation, TMD is able to increase the mitogen-induced T-cell proliferation.

To evaluate the effects of thymomodulin (TMD), a thymic biological response modifier derived from calf thymus, on the release of various cytokines involved in the lung immune reactions, human alveolar macrophages (AM) and peripheral blood lymphocytes (PBL) were cultured either alone or in co-cultures. In co-cultures of AM with PBL, TMD did not induce any change in gamma-interferon (gamma-IFN) and interleukin-1 (IL-1) secretion, while it was able to increase the level, of tumour necrosis factor (TNF) (TMD 100 micrograms.m-1, p < 0.05 vs control cultures), and of granulocyte macrophage colony-stimulating factor (GM-CSF) (TMD 1, 10 and 100 micrograms.ml-1 p < 0.05, < 0.05 and < 0.01, respectively, vs control cultures). In cultures of AM alone, TMD did not induce changes in the levels of any of the tested cytokines, whilst in supernatants from PBL lymphocyte cultures, TMD at 1, 10 and 100 micrograms.ml-1 increased the amounts of GM-CSF (p < 0.01 each comparison vs control cultures). Thus, TMD seems to directly stimulate lymphocytes to secrete GM-CSF and to modulate macrophage-lymphocyte interactions, resulting in the release of TNF and GM-CSF.