Platelets, in addition to exerting hemostatic activity, contribute to immunity and inflammation. The recent report that platelets express CD40 led us to hypothesize that CD40 ligand (CD40L)-positive T cells could bind to platelets, cause their activation, and trigger granular RANTES release, creating a T cell recruitment feedback loop. Platelets were cocultured with resting or activated autologous T cells and their activation was assessed by P-selectin expression. RANTES binding to endothelial cells was assessed by confocal microscopy, and its biological activity was demonstrated by a T cell adhesion assay. CD40L-positive T cells induced platelet activation through a contact-mediated, CD40-dependent pathway resulting in RANTES release, which bound to endothelial cells and mediated T cell recruitment. Soluble CD40L induced the same events via p38, but not extracellular signal-regulated kinase, phosphorylation. These results show the existence of a novel platelet-dependent pathway of immune response amplification which brings these nonimmune cells close to the level of pathogenic relevance traditionally attributed to classical immune cells.

Mucosal immune tolerance in the healthy intestine is typified by lamina propria T cell (LPT) functional hyporesponsiveness after TCR engagement when compared with peripheral blood T cell (PBT). When LPT from an inflamed intestine are activated through TCR cross-linking, their responsiveness is stronger. LPT are thus capable of switching from a tolerant to a reactive state, toggling between high and low thresholds of activation. We demonstrate that in normal LPT global tyrosine phosphorylation upon TCR cross-linking or an increase in intracellular H2O2, an inhibitor of protein tyrosine phosphatases, is muted. Thus, we propose that LPT have a greater reducing capacity than PBT, shifting the balance between kinases and protein tyrosine phosphatases in favor of the latter. Surface γ-glutamyl transpeptidase, an indirect indicator of redox potential, and glutathione are significantly elevated in LPT compared with PBT, suggesting that elevated glutathione detoxifies TCR-induced reactive oxygen species. When glutathione is depleted, TCR-induced LPT tyrosine phosphorylation rises to PBT levels. Conversely, increasing glutathione in PBT attenuates tyrosine phosphorylation. In LPT isolated from inflamed mucosa, TCR cross-linking induces greater phosphorylation, and γ-glutamyl transpeptidase levels are reduced compared with those from autologous noninflamed tissue. We conclude that the high TCR signaling threshold of mucosal T cells is tuned by intracellular redox equilibrium, whose dysregulation may mediate intestinal inflammation.

BackgroundAn association of acetaminophen use and asthma was observed in the International Study of Asthma and Allergies in Childhood study. However there are no clear mechanisms to explain an association between acetaminophen use and immunologic pathology. In acidic conditions like those in the stomach and inflamed airway, tyrosine residues are nitrated by nitrous and peroxynitrous acids. The resulting nitrotyrosine is structurally similar to 2,4-dinitrophenol and 2,4-dinitrochlorobenzene, known haptens that enhance immune responses by covalently binding proteins. Nitrated acetaminophen shares similar molecular structure.ObjectiveWe hypothesized the acetaminophen phenol ring undergoes nitration under acidic conditions, producing 3-nitro-acetaminophen which augments allergic responses by acting as a hapten for environmental allergens.Methods3-nitro-acetaminophen was formed from acetaminophen in the presence of acidified nitrite, purified by high performance liquid chromatography, and assayed by gas-chromatography mass spectrometry. Purified 3-nitro-acetaminophen was reacted with Dermatophagoides pteronyssinus (Der p1) and analyzed by mass spectrometry to identify the modification site. Human peripheral blood mononuclear cells proliferation response was measured in response to 3-nitro-acetaminophen and to 3-nitro-acetaminophen-modified Der p1.ResultsAcetaminophen was modified by nitrous acid forming 3-nitro-acetaminophen over a range of different acidic conditions consistent with airway inflammation and stomach acidity. The Der p1 protein-hapten adduct creation was confirmed by liquid chromatography-mass spectrometry proteomics modifying cysteine 132. Peripheral blood mononuclear cells exposed to 3-nitro-acetaminophen-modified Der p1 had increased proliferation and cytokine production compared to acetaminophen and Der p1 alone (n = 7; p < 0.05).ConclusionThese data suggests 3-nitro-acetaminophen formation and reaction with Der p1 provides a mechanism by which stomach acid or infection-induced low airway pH in patients could enhance the allergic response to proteins such as Der p1.