Abstract
BackgroundBrain injury (BI) induces a state of immunodepression leading to pneumonia. We investigated the invariant natural killer T (iNKT) cell compartment.MethodsThis is an observational study in two surgical intensive care units (ICUs) of a single institution and a research laboratory. Clinical data and samples from a prospective cohort were extracted. Severe brain-injured patients (n = 33) and sex- and age-matched healthy donors (n = 40) were studied.ResultsWe observed the presence of IL-10 in serum, a loss of IFN-γ and IL-13 production by peripheral blood mononuclear cells (PBMCs) following IL-2 stimulation, and downregulation of HLA-DR expression on both monocytes and B cells early after BI. Inversely, CD1d, the HLA class I-like molecule involved in antigen presentation to iNKT cells, was over-expressed on patients’ monocytes and B cells. The antigen-presenting activity to iNKT cells of PBMCs was increased in the patients who developed pneumonia, but not in those who remained free of infection. Frequencies of iNKT cells among PBMCs were dramatically decreased in patients regardless of their infection status. Following amplification, an increased frequency of CD4+ iNKT cells producing IL-4 was noticed in the group of patients free of infection compared with those who became infected and with healthy donors. Finally, serum from BI patients inhibited the iNKT cells’ specific response as well as the non-specific IL-2 stimulation of PBMCs, and the expression of the beta-2 adrenergic receptor was elevated at the surface of patients T lymphocytes.ConclusionsWe observed severe alterations of the iNKT cell compartment, including the presence of inhibitory serum factors. We demonstrate for the first time that the decreased capacity to present antigens is not a generalized phenomenon because whereas the expression of HLA-DR molecules is decreased, the capacity for presenting glycolipids through CD1d expression is higher in patients.
Highlights
Susceptibility to nosocomial infections, mainly pneumonia [1,2,3] after an acute brain injury (BI) [4], is correlated with an acute immunodepression [5,6,7]
T cell receptor (TCR) recognition is restricted by the monomorphic MHC class-Ilike molecule CD1d that is expressed by antigenpresenting cells (APC) [11]
We previously demonstrated that traumatic brain injury (TBI) and sub-arachnoid hemorrhage (SAH) displayed an immune dysfunction characterized by an attenuated granulomatous immune response ex vivo [7]
Summary
Susceptibility to nosocomial infections, mainly pneumonia [1,2,3] after an acute brain injury (BI) [4], is correlated with an acute immunodepression [5,6,7]. T cell receptor (TCR) recognition is restricted by the monomorphic MHC class-Ilike molecule CD1d that is expressed by antigenpresenting cells (APC) [11]. Several subsets of iNKT cells have been described based on their expression of the CD4 or CD8 molecules. They can be CD4+/CD8−, CD4−/CD8+, or CD4−/CD8− [12], the CD4+ subset likely representing less mature cells [13, 14]. The type of response to which they contribute is largely dependent upon the context and the APCs with which they interact They are efficient to drive the first stages of innate responses [14]. We investigated the invariant natural killer T (iNKT) cell compartment
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