Human primary adenotonsillar naïve phenotype CD45RA CD4 T lymphocytes undergo apoptosis upon stimulation with a high concentration of CD3 antibody.

Young children need to develop immune tolerance to harmless foreign antigens such as digested nutrients and various inhaled airborne antigens. Because of its anatomical location, pharyngeal adenotonsillar tissue is a potential site for the establishment of this immune tolerance. To characterize possible mechanisms of peripheral immune tolerance, we studied human primary adenotonsillar naïve phenotype CD45RA(+) CD4(+) T cells, which represent cells that have not previously encountered foreign antigens. It was found that these CD45RA(+) CD4(+) T cells expressed higher levels of the activation marker CD69 as compared with peripheral blood CD45RA(+) CD4(+) T cells. Upon stimulation with a high concentration of CD3 antibody, which mimics the encounter of a high antigen dose, adenotonsillar CD45RA(+) CD4(+) T lymphocytes, but not peripheral blood CD45RA(+) CD4(+) T cells, underwent apoptosis. After 6 h stimulation with a high concentration of CD3 antibody, over 25% of the cells were apoptotic. Interfering with the Fas-FasL interaction with recombinant Fas or an antibody against Fas-ligand partially inhibited apoptosis. Our study results suggest that high concentrations of antigens, such as various nutrients and airborne antigens, may induce peripheral immune tolerance by selectively deleting naïve phenotype CD45RA(+) CD4(+) T cells via T-cell receptor-triggered apoptosis in human adenotonsillar tissue.

Reactive oxygen species induce signals that lead to apoptotic DNA degradation in primary CD4+ T cells.

Reactive oxygen species are toxic to cells but they may also have active roles in transducing apoptotic events. To study the role of reactive oxygen species in growth factor depletion induced apoptosis of human primary CD4+ T cells, we used a synthetic manganese porphyrin superoxide dismutase mimetic to detoxify superoxide anions formed during apoptosis. Apoptosis of primary CD4+ T cells was characterized by generation of superoxide anions, plasma membrane phosphatidyl-serine translocation, loss of mitochondrial membrane potential, activation of caspase 3, condensation of chromatin, as well as DNA degradation. The detoxification of superoxide anions did not influence plasma membrane phosphatidyl-serine translocation, or chromatin condensation, and only marginally inhibited the loss of mitochondrial membrane potential and the formation of DNA strand breaks. In contrast, the detoxification of superoxide anions significantly reduced caspase 3 activity and almost completely inhibited the apoptotic decrease in total cellular DNA content as measured by propidium iodide staining. Our results indicate that reactive oxygen anions induce signals leading to efficient DNA degradation after the initial formation of DNA strand breaks. Thus, reactive oxygen anions have active roles in signaling that lead to the apoptotic events.

Platelet endothelial cell adhesion molecule-1 is expressed in adenoidal crypt epithelial cells.

The adenoidal epithelial crypt is a potential site of antigen transport from pharyngeal lumen to adenoidal tissue. The base of the crypt is consistently infiltrated with leucocytes, forming a reticular lymphoepithelial structure. To evaluate mechanisms that possibly mediate leucocyte infiltration, expressions of leucocyte adhesion molecules, such as platelet endothelial cell adhesion molecule-1 (PECAM-1) (CD31), vascular cell adhesion molecule-1 (VCAM-1) (CD106) and intercellular adhesion molecule-1 (ICAM-1) (CD54), were studied in the adenoidal epithelial crypt. Epithelial cells in the outer opening of the adenoidal crypt were positive for VCAM-1, whereas epithelial cells at the base of the crypt were positive for PECAM-1. Isolated ICAM-1-expressing cells were found throughout the epithelial crypt. Double immunofluorescence staining revealed that the epithelial cells positive for PECAM-1 or VCAM-1 were positive for cytokeratin. The expression of PECAM-1 in the base and VCAM-1 at the orifice of the adenoidal epithelial crypt implies that the base and the orifice of the crypt have a distinct ability to recruit leucocytes. Epithelial cells expressing PECAM-1 may have a role in the formation of the reticular lymphoepithelial structure in the epithelial crypt.