Secretion of Antimycobacterial Fatty Acids by Normal and Activated Macrophages

Abstract

Cellular resistance to facultative intracellular parasites has been studied by determining the antimycobacterial activity and the amount of fatty acids in sera and in heptane extracts of freshly collected and 24-h-cultured normal and activated guinea pig alveolar macrophages and liver cells. The quantity and the antimycobacterial activity of extractable fatty acids were determined by gas chromatography and the agar plate diffusion test, respectively. These determinations showed that heptane extracts of activated cells inhibited the growth of BCG much more effectively than fractions prepared from normal cells; chromatographic analyses showed that extracts of activated cells contained six times more C16 and C18 long-chain fatty acids than did fractions of normal cells. Heptane extracts of 24-h-cultured cells and of their media showed that during incubation normal and activated cells release fatty acids into the culture media without apparent cell injury; in all experiments liver cells produced larger amounts of fatty acids than alveolar macrophages. Sera collected from activated guinea pigs inhibited the growth of BCG and contained two to five times more total fatty acids than did the growth-supporting normal serum. That bactericidal fatty acids are excreted into the tissue culture medium of incubated cells or into the blood of immunologically stimulated animals suggests that macrophages can exert antibacterial effects without phagocytosis.

Further study on the roles of the effector molecules of immunosuppressive macrophages induced by mycobacterial infection in expression of their suppressor function against mitogen-stimulated T cell proliferation

“…Macrophages activated by mycobacterial infection release a large amount of FFA [24], which are known to cause inhibition of mitogen-induced T lymphocyte proliferation [8,25]. Oleic acid is also known to perturb transmembrane signallings of T cells, such as Con A-induced Ca 2þ influx [26], presumably due to a physical perturbation of membrane lipid.…”

Bactericidal Effect of Fatty Acids on Mycobacteria, with Particular Reference to the Suggested Mechanism of Intracellular Killing

“…The mycobactericidal effect of long-chain fatty acids has long been known and many studies have been conducted to determine the role of fatty acids in the defense mechanism in mycobacterial infections (5,9,10,18,(21)(22)(23)30). Theoretically, there are three spaces for the killing of mycobacteria in vivo; i.e., extracellular space, phagosome and phagolysosome.…”

“…Theoretically, there are three spaces for the killing of mycobacteria in vivo; i.e., extracellular space, phagosome and phagolysosome. Hemsworth and Kochan (10) reported the pos- sible extracellular killing of mycobacteria by fatty acids secreted by macrophages. However, because of the strong reversal effect of serum on the bactericicdal activity of fatty acids and also because of the continuous streaming of extracellular fluids, it is doubtful that the required concentrations of fatty acids can be obtained in the extracellular space.…”

“…In the case of M. smegmatis ATCC 607 palmitic and stearic acids showed a very weak bactericidal effect (Table 1), although M. tuberculosis is more sensitive to palmitic acid (22). Since the main fatty acids secreted by macrophages are oleic, linoleic, palmitic, and stearic acids (6,10,28), the effect of coexistence with saturated fatty acids on the bactericidal activity of unsaturated fatty acids was examined. The addition to an unsaturated fatty acid (oleic or linoleic acid) of five times its concentration of a saturated fatty acid (palmitic or stearic acid) did not very strongly inhibit the bactericidal activity of the unsaturated fatty acid at pH 5.0 to 7.0, except in the case of oleic acid at pH 7.0.…”

“…However, pathogenic mycobacteria are generally resistant to the action of lysozyme and immunologically activated macrophages are required to kill them, suggesting that some other bactericidal substance(s) damages mycobacteria moreefficiently in activated macrophages than in normal macrophages. As mycobatericidal substances, superoxide anion (O2-) (1,12,16), hydrogen peroxide (H2O2) (12-16, 20, 32), and free fatty acids (5,9,10,18,(21)(22)(23)30) have been studied extensively and a phagolysosome is proposed as thespace in which mycobacteria are killed . The ability of some pathogenic mycobacteria to inhibit phagosome-lysosome fusion is presumed to be related to their pathogenicity (8,26,27).…”