Live Brucella spp. fail to induce tumor necrosis factor alpha excretion upon infection of U937-derived phagocytes

Abstract

Tumor necrosis factor alpha (TNF-a) plays a central role in activation of first-line defenses of a host against foreign organisms. To determine whether Bruceila infection modulated TNF-aL production, we measured the biological activity of this cytokine in supernatants of U937 cell-derived macrophages and of fresh human monocytes infected with Brucella spp. Neither the smooth nor rough Bruceila strains used induced any measurable TNF-a excretion upon infection. On the contrary, as reported before for other gram-negative bacteria, phagocytosis of nonpathogenic Escherichia coli was followed by a rapid and transient induction of TNF-a release, suggesting an involvement of this cytokine in some autocrine process. As expected, the Brucella strains tested survived and/or multiplied within U937-derived macrophages, whereas E. coli was rapidly eliminated after phagocytosis. Immunoglobulin G opsonization of E. coli strains enhanced their intracellular killing and strongly potentiated TNF-a secretion. Immunoglobulin G opsonization of Bruceila strains, in contrast, did not lead to TNF-a production, although their rate of intracellular multiplication was reduced. Killed brucellae, however, promoted a significant excretion of TNF-at from U937-derived macrophages into cell culture supernatants. We finally demonstrated that pretreatment of U937-derived macrophages with exogenous TNF-a significantly inhibited intracellular multiplication of Brucella spp. These results and experiments performed on fresh human monocytes or with isolated lipopolysaccharide (LPS) showed that (i) differences in

Characterization of Biological Activities of Brucella melitensis Lipopolysaccharide

“…The lower biological activities of B. melitensis LPS may be based on the lipid A structure. Incidentally, the low biological activities of B. abortus LPS have been already reported (4,13,25,30) and are explained by the peculiar lipid A structure (22,30).…”

“…Further, the O antigen of Brucella LPS is a homopolymer of perosamine (4,6dideoxy-4-formamido-d-mannopyranosyl) (3,27,37). The biological activities such as cytokine production and lethality of S-LPS and rough types of LPS (R-LPS) from various Brucella strains are reported to be lower than those of enterobacterial LPS (4,14,25,29). The lower endotoxicity seems to be responsible for the unique lipid A structure of Brucella LPS.…”

A beneficial aspect of a CB1 cannabinoid receptor antagonist: SR141716A is a potent inhibitor of macrophage infection by the intracellular pathogen Brucella suis

“…Infection of human monocytes, THP-1-derived monocytes, or mouse J774A.1 cells with B. suis was performed, as described [28][29][30], in 24-well plates (Falcon, Becton Dickinson, Meylan, France). Briefly, bacteria were centrifuged and resuspended in RPMI-1640.…”

“…The gentamicin concentration was sufficient to kill bacteria within 60 min and did not impair the intracellular multiplication of Brucella. At various post-infection times, culture supernatant was removed and the number of intracellular viable bacteria evaluated by colony-forming unit (CFU) determination from replicate plates and serial dilutions of cell homogenates as previously described [28].…”

“…Moreover, if as mentioned previously [24,25], CB receptor endogenous agonists are produced by leukocytes, they might inhibit macrophage activation and help intracellular bacteria to circumvent the host defense. We thus investigated the influence of CB ligands on models of human and murine macrophage infection by the facultative intracellular gram-negative bacteria Brucella suis [28][29][30]. Nonselective CB1/CB2 cannabinoid receptor agonists (CP55,940 or WIN 55212-2 [1]) and specific antagonists of CB1 (SR141716A [26]) and CB2 (SR144528 [27]) receptors were assayed.…”