Low response of BALB/c macrophages to priming and activating signals.

Trehalose dimycolate (TDM), a mycobacterial glycolipid, is a powerful macrophage-priming agent. However, its efficiency seems limited in the case of BALB/c mice. Peritoneal macrophages harvested from TDM-treated BALB/c mice did not control BCG growth in vitro as efficiently as similar macrophages from two other mouse strains, (B6 x D2)F1 and C57BL/6, which are respectively Bcgr and Bcgs. BALB/c macrophages elicited by TDM also exhibited a low capacity to produce hydrogen peroxide and, after activation by lipopolysaccharide (LPS), weak cytostatic activity against P815 mastocytoma cells. Finally, alkaline phosphodiesterase, a marker of resident and inflammatory macrophages, was still expressed at a high level in macrophages of BALB/c mice treated with TDM. Low responsiveness of BALB/c macrophages to stimuli was not observed with TDM only; activation for tumor cytotoxicity of thioglycolate-elicited macrophages from BALB/c mice required also higher doses of interferon-gamma, and LPS. L-Arginine-dependent production of nitric oxide was inducible in macrophages from BALB/c mice, but the conditions required for its induction were more stringent. Thus, the reduced antiproliferative effects of BALB/c macrophages may be due to uncomplete induction of NO synthase after suboptimal stimulation.

Stimulation of antimycobacterial activity in mouse peritoneal macrophages by priming with trehalose dimycolate (TDM).

We examined the potential of two bacterial immunomodulators, trehalose dimycolate (TDM) and lipopolysaccharide (LPS), to stimulate the capacity of mouse peritoneal macrophages to control the growth of the intracellular bacterium, Mycobacterium tuberculosis BCG. Macrophages were obtained from mice innately susceptible (Bcgs) or resistant (Bcgr) to BCG infection. In all mouse strains tested (Bcgr and Bcgs), with the exception of BALB/c (Bcgs), TDM was sufficient to elicit macrophages with strong antimycobacterial activity in vitro. In BALB/c mice, the induction of anti-BCG activity required two signals, TDM and LPS, given in sequence. Our data suggest that additional gene(s), besides the Bcg locus, control macrophage resistance to BCG.

Modifications of glycosylation patterns in macrophages upon activation.

Activated macrophages, in contrast to inflammatory and resident macrophages, are able to inhibit the growth of intracellular pathogens and tumor cells. In order to understand the adaptative changes which allow macrophages to express antitumor activity, we compared, among several parameters, the glycoproteins of cytotoxic and non-cytotoxic macrophages. After activation of mouse peritoneal macrophages by two stimuli applied in a sequence (trehalose dimycolate in vivo, lipopolysaccharide in vitro), we observed that: (1) surface sialic acid residues (labeled by tritiated borohydride after treatment of intact cells in culture by periodate) were reduced by 37%; (2) total sialic acid, as measured by an adaptation to HPLC of the thiobarbituric assay, was reduced by 30%. Variations in the intensity of the labeling after periodate/borohydride treatment were especially pronounced for a few high-molecular-weight glycoproteins. Analysis of glycopeptides indicated that the reduction of sialylation was accompanied by a slight increase in the relative importance of high mannose-type oligosaccharides (glycopeptides sensitive to endoglycosidase H or retained on concanavalin A-Sepharose) but did not affect the ratio of the various anionic species separated on QAE-Sephadex. A reduced sialylation of glycans after activation may facilitate interactions of macrophages with microbes and tumor cells.