1. The final stages of T cell development occur in the thymic medulla, after the
ID: 204100 • Letter: 1
Question
1. The final stages of T cell development occur in the thymic medulla, after the developing cells become CD4 or CD8 single-positive. One important change that occurs during this final maturation is:
A. The down-regulation of the pre-T-cell receptor alpha(pre-Talpha) chain protein
B. The up-regulation of genes encoding effector cytokines and cytolytic effector proteins
C. The increased susceptibility to T-cell receptor-induced apoptosis
D. The loss of susceptibility to T-cell receptor-induced apoptosis
E. The up-regulation of signaling proteins required for T cell activation
2. Experimental mouse models have been developed to study the mechanisms leading to the breakdown of self-tolerance and the onset of autoimmunity. One strategy is to express a foreign antigen, such as a viral protein, in a single defined cell type in a peripheral organ. For instance, the lymphocytic choriomeningitis virus (LCMV) glycoprotein has been expressed in -islet cells of the pancreas by making a line of mice that is transgenic for a construct linking the LCMV-glycoprotein gene to the insulin promoter. In these transgenic mice, the LCMV protein is expressed only in pancreatic beta-islet cells. Thymocytes with T-cell receptors specific for a peptide of LCMV-glycoprotein bound to MHC class I develop normally in the thymus, and do not undergo negative selection. The fate of these T cells once they emigrate from the thymus would likely be:
A. They would be activated in the periphery and attach and kill the pancreatic beta-islet cells.
B. They would either be deleted in the periphery or would become unresponsive.
C. They would induce an inflammatory response in the pancreas that would up-regulate co-stimulatory molecules on antigen-presenting cells.
D. They would secrete cytokines that promote T cell proliferation.
E. They would differentiate into virus-specific memory T cells that would protect mice upon infection with LCMV.
3. Strep throat is commonly caused by group A Streptococcus bacteria. A common symptom of strep throat is the presence of swollen lymph nodes in the neck. This symptom usually peaks about 2–4 days after the onset of the infection, and is due to:
A. Damage to the pharyngeal epithelium by the bacteria
B. Release of bacterial PAMPs leading to inflammatory cytokine production
C. Trapping and activation of antigen-specific lymphocytes in the lymph nodes of the neck
D. Recruitment of neutrophils to the lymph nodes of the neck
E. Recruitment of circulating macrophages to the lymph nodes of the neck
Explanation / Answer
1) The increased susceptibility to T-cell receptor-induced apoptosis - In medulla, negative selection of T cells occurs. The TCR that strongly recognizes self MHC die of apoptosis resulting in self tolerance. Positive selection occurs in the cortex resulting in MHC restriction.
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