SUMMARY As Q fever is associated with an inflammatory syndrome, we determined circulating levels of inflammatory cytokines, cytokine antagonists, and activation markers of leucocytes in patients with acute Q fever and Q fever endocarditis. Tumour necrosis factor (TNF) and IL-6, but not IL-1β, were markedly increased compared with controls. Cytokine antagonists and activation markers of leucocytes were profoundly different in acute and chronic Q fever. IL-1 receptor antagonist and TNF receptor type II were significantly increased in patients with acute Q fever, suggesting a shift of cytokine balance towards cytokine antagonists. The activation marker of B cells, sCD23, was significantly increased in Q fever endocarditis compared with controls and patients with acute Q fever. In a 2-year follow-up study of patients with Q fever endocarditis, sCD23 and specific IgG levels slowly decreased in patients whose symptoms resolved, but remained high in those who required prolonged treatment.
La reponse immunitaire est le fruit d'un dialogue intermoleculaire: le tcr qui assure la specificite de la reponse reconnait l'ag en association avec les molecules du cmh. Simultanement les co-recepteurs cd4 ou cd8 reconnaissent la partie monomorphe des molecules de classe ii ou de classe i du cmh, respectivement. Parallelement, les molecules dites accessoires transmettent des signaux de co-stimulation apres engagement avec leur ligand specifique. L'ensemble de ces phenomenes necessite un etroit controle pour eviter les reactions excessives. Les molecules de classe i exprimees a la surface des lymphocytes t murins, pourraient aussi intervenir au cours de ces etapes regulatrices. En effet, les ac specifiques des domaines alpha 1 et alpha 2 de ces molecules inhibent la proliferation des lymphocytes t, en reponse primaire uniquement. Ces resultats suggerent que les molecules de classe i, comme d'autres molecules accessoires ne sont plus necessaires au cours des reponses secondaires. A l'aide de souris transgeniques dont les cellules expriment les molecules de classe i qa-2, ancrees dans la membrane par un phosphatidyl inositol, on a mis en evidence que les parties intracytoplasmique et transmembranaire des molecules de classe i ne sont pas impliquees dans la transmission du signal. Il semblerait donc que les molecules de classe i soient associees par leur domaine extracytoplasmique a une ou plusieurs autres molecules qui transmettent ce signal. La fixation des ac sur ces molecules de classe i induirait la dissociation avec cette ou ces molecule(s) en cis empechant ainsi la transmission du signal. De plus, la presence des molecules de classe i lors de la signalisation induite par les molecules thy-1 semble indispensable, ce qui implique que les molecules thy-1 font partie d'un complexe multimoleculaire forme par les molecules de classe i et la ou les molecule(s) transmettant le signal. D'autre part, les ac diriges contre les molecules de classe i semblent inhiber l'etape d'activation de la pkc car les etapes en amont telles que le flux calcique ou la phosphorylation precoce des tyrosines sont normaux alors que tous les evenements qui suivent l'activation de la pkc sont inhibes en presence des ac diriges contre les molecules de classe i. L'ensemble de ces resultats nous montre que les molecules de classe i jouent effectivement un role au cours de l'activation des lymphocytes t murins, en formant un complexe multimoleculaire capable de transmettre des signaux aux cellules t
Murine T and B splenocytes were incubated with antibodies that recognize CD3 or surface IgM. These antibodies induced proliferation of their respective target cells. Once stimulated via their receptors, the proliferation of both CD4+ and CD8+ T but not B lymphocytes was inhibited by class I-specific antibodies or their monovalent Fab' fragments. The inhibition of proliferation was dependent on the site on class I molecules recognized by the antibodies used, with the alpha 1/alpha 2 domains of H-2K molecules representing the major site for inhibition. Only soluble antibody-mediated proliferation could be inhibited by class I-directed antibodies; proliferation induced by CD3-specific antibody immobilized on plastic was not inhibited. Primary allogeneic MLR was also inhibited by class I-specific antibodies. In contrast, neither secondary allogeneic MLR, secondary Ag-specific responses, nor proliferation of CTL clones or tumor cell lines were inhibited by class I-specific antibodies. These results suggest a role for class I molecules in regulation of TCR/CD3- but not surface IgM-mediated cell signaling, which depends on the form of stimulation and the stage of differentiation of T cells.
Q fever is an infectious disease caused by Coxiella burnetii, an obligate intracellular microorganism that inhabits monocytes/macrophages. The dysregulated production of TNF-alpha in Q fever endocarditis has been associated with defective killing of C. burnetii by patient monocytes. As soluble receptors for TNF-alpha (TNF-R55 and TNF-R75) regulate TNF-alpha activity, we investigated their release by monocytes in Q fever. Spontaneous and C. burnetii-stimulated release of TNF-R75, but not of TNF-R55, was up-regulated in patients with ongoing endocarditis compared with controls. The increase in TNF-R75 release was related to the activity of Q fever endocarditis, since TNF-R75 release was similar in patients with cured endocarditis and controls. While spontaneous release of TNF-R75 by monocytes from patients with ongoing Q fever endocarditis occurred without changes in its membrane expression, C. burnetii increased the surface expression of TNF-R75. In addition, TNF-R75 transcripts were increased in resting and C. burnetii-stimulated monocytes from patients with ongoing endocarditis. On the other hand, TNF-R75 release was not related to TNF-alpha secretion. These results indicate that the modulation of TNF-R75 is a critical feature of the pathophysiology of Q fever endocarditis.
We have reported that class I- [and lymphocyte function-associated antigen-1 (LFA-1-)] specific monoclonal antibodies (mAb) inhibit anti-CD3-mediated activation of naive T cells. The present study investigated the mechanism of this inhibition. CD28-specific mAb augmented stimulation induced by soluble CD3 mAb, but this costimulation was also inhibited by anti-class I or anti-LFA-1 mAb. However, stimulation of T cells was not inhibited when activated B cells were present. Neither B7-1- nor B7-2-specific blocking mAb or soluble CTLA-4, CD40 or gp39 restored the inhibition. Thus, other molecules expressed on activated B cells are implicated for T-cell activation, which could compensate blockade of class I or LFA-1 molecules. Inhibition induced by class I-specific mAb could potentially be mediated through extracellular, transmembrane or cytoplasmic domains of the target molecules. These possibilities were evaluated by the use of mice transgenic for the Qa-2 molecule, selected for expression of Qa-2 at levels equivalent to classical class I molecules. Qa-2 is inserted in the membrane through phosphatidylinositol linkages. Antibodies directed to Qa-2 inhibited CD3-induced stimulation, demonstrating that cytoplasmic and transmembrane protein sequences of class I molecules are not necessary for the inhibitory effect. Inhibition thus presumably depends on extracellular domains. Finally, T cells from beta 2-microglobulin knock-out mice responded to CD3-specific mAb as well as their class I-positive littermates. Nevertheless, stimulation of T cells from these mice with mitogenic anti-Thy-1 mAb was markedly reduced. Signalling by Thy-1 and the CD3 complex may normally occur through pathways in which class I molecules are implicated.
