Role of Monocytes in the Up‐Regulation of the Early Activation Marker CD69 on B and T Murine Lymphocytes Induced by Microbial Mitogens

Abstract

CD69 is an early marker of lymphoid cell activation. The authors report on an up-regulation of CD69 in splenic B and T cells of C57Bl/6 mice after administration of lipopolysaccharide (LPS) or microbial immunosuppressive/mitogenic (ISM) proteins produced by C. albicans (p43) and African Swine Fever Virus (p36). This up-regulation of CD69 was observed 6 and 24 h after mitogenic treatments. The same pattern of increased CD69 expression was observed in the lymph nodes of mice treated with p43 or LPS, whereas p36 treatment failed to induce increased CD69 expression in this organ. Intracellular calcium mobilization was induced in splenic B and T lymphocytes after incubation of total spleen cells with LPS, p43 or p36. This increase was higher in B than in T cells. Increased calcium mobilization was also seen in lymph node B cells after incubation with p43 or p36 and in lymph node T cells after p43 stimulation. Up-regulation of CD69 expression on B and T cells was also observed after in vitro stimulation of spleen cells with the three mitogens used. Similar results were obtained with culture supernatants of macrophage/monocyte (M phi) cells activated with LPS (LPS/M phi CS). Stimulation of M phi cells with LPS or with the ISM proteins is demonstrated by the increased production of nitrites by these cells. The increased in vitro expression of CD69 was, however, not abolished by monoclonal antibodies to M phi cytokines such as IL-6, IL-10 or TNF alpha. No increased expression of CD69 was found in vitro on purified B or T cells, even when mixed upon stimulation with p43, p36, LPS or with LPS/M phi CS. However, an increase in the expression of CD69 was observed on B cells co-cultured with M phi cells after treatment with LPS or p36. All three mitogens failed to induce increased CD69 expression on cultured T cells mixed with M phi cells.

TLR2 is expressed on activated T cells as a costimulatory receptor

“…(iii) Although activated CD4 ϩ T cells expressed similar levels of TLR4 and TLR2, the cells did not respond to LPS, a recognized ligand for TLR4 (33). This is consistent with a large number of reports in the literature (34)(35)(36). LPS has recently been reported to activate CD4 ϩ CD25 ϩ T cells in mice (32).…”

Pegylated Alpha Interferon Is an Effective Treatment for Virulent Venezuelan Equine Encephalitis Virus and Has Profound Effects on the Host Immune Response to Infection

“…Such a rapid high expression of CD69 has been described in other models of virus infection in which viral antigens from either mouse mammary tumor virus, rhinovirus, or African swine fever virus induced high CD69 expression among various lymphocyte populations (8,39,42).…”

“…Other studies of virus-induced nonspecific cell activation have suggested that macrophages or monocytes induce this nonspecific expression of CD69 via the secretion of soluble factors in situ (8,39). VEEV E2 expression seemed to be restricted to the splenic macrophage population in both untreated and PEG IFN-␣-treated mice.…”

The presence of CD8+ invariant NKT cells in mice

“…These data suggest that CD8 + iNKT cells probably have a more Th1-skewed phenotype than conventional CD8 -iNKT cells. Secondly, we examined the activation status of NKT cells by measuring CD69 on NKT cells upon α-GalCer stimulation, since it was previously reported that α-GalCer stimulation of NKT cells leads to significant up-regulation of CD69 on NKT cells (Testi et al, 1994;Vilanova et al, 1996). CD8 + iNKT cells up-regulated CD69 as much as CD8 -iNKT cells upon α-GalCer stimulation, suggesting that CD8 + iNKT cells have the same activation potency as CD8 -iNKT cells ( Figure 3B).…”