Exam 9: T-Cell-Mediated Immunity

Naive T cells scan the dendritic cells in the cortical region of the lymph node as they migrate. The initial encounter of T cells with dendritic cells is mediated by interactions between the T-cell receptor and the peptide:MHC complexes on the dendritic cell.

Cytotoxic effector T cells also produce inflammatory cytokines such as IFN- $\gamma$ and TNF- $\alpha$ when their T-cell receptor recognizes peptide:MHC on a target cell. One effect of this cytokine secretion is to enhance the ability of CD8 effector T cells to recognize and kill other infected cells in the nearby vicinity. This enhanced activity is due to:

The TNF family of cytokines and their receptors are critical for the development of secondary lymphoid organs, such as the lymph nodes and Peyer's patches. As a consequence, knockout mice lacking expression of LT- $\beta$ fail to develop most of these structures. Reconstitution of irradiated LT- $\beta$ -deficient mice with bone marrow stem cells from wild-type mice (e.g., LT- $\beta$ -sufficient) would:

Most effector T cells migrate out of secondary lymphoid organs and into tissues to exert their function. In which of the cases shown in Figure will the T_H1 effector cell undergo long-lived interactions with its target cell, an infected macrophage? Assume all of the target cells shown below are infected with the pathogen recognized by the specific T_H1 cells.

A mouse line (called 'Wm') is discovered that has an unexpected immunodeficiency. Genetic studies indicate that the immunodeficiency is due to a single gene defect. The Wm mice have normal numbers of all immune cell lineages, including T cell, B cells, macrophages, dendritic cells, NK cells, and granulocytes. When infected with viruses or intracellular bacteria and protozoa, the Wm mice mount normal protective T cell responses and clear the infections. However, given a helminthic parasite infection, the Wm mice cannot clear the infection and succumb to the disease. A set of wild-type (WT) and Wm mice were infected with the helminthic parasite, Nippostrongylus brasiliensis, and cytokine production by the CD4 T cells was analyzed. For this experiment, CD4 T cells were isolated from mice at day 8 post-infection, stimulated in vitro for 24 hr stimulation with anti-CD3 antibody to elicit cytokine secretion, and then cytokine levels in the culture supernatants were examined by ELISA. The results are shown in Figure. a) What process is likely defective in the Wm mice? b) Which molecules are the best candidates for the defective gene in Wm mice? Note that the transcription factor GATA-3 is not a likely candidate gene, as GATA-3-deficient mice have an early block in T cell development in the thymus, and completely lack all T cells.and Wm mice and were stimulated in vitro with anti-CD3 plus anti-CD28 antibodies, in the presence of additional cytokines and blocking antibodies as indicated. After three days of stimulation, the T cells are isolated, washed, and restimulated with anti-CD3 antibody in medium lacking any cytokines or antibodies. After 24 hr, the cytokines present in the supernatants of these restimulated CD4 T cells are examined by ELISA. These data are show in Figure. c) Do these results change your answers to parts (a) or (b) above? To continue to identify the molecule or pathway defective in Wm T cells, CD4 T cells are isolated from Wm mice and stimulated in vitro with anti-CD3 + anti-CD28 antibodies in the presence of IL-4 and anti-IFN- $\gamma$ antibody, as above. One day later, the cells are transduced with a vector expressing the transcription factor GATA3. From this vector, GATA3 will be expressed constitutively and at high levels, in all of the T cells. As a control, an 'empty' vector (not containing GATA-3) is also transduced into Wm CD4 T cells. Three days later, the cells are washed and restimulated for cytokine secretion analysis by ELISA, as above. Additionally, flow cytometry analysis of naive wild-type and Wm CD4 T cells stained with an antibody to the IL-4 receptor was performed, and the results are shown.and Wm CD4 T cells was then performed to examine the expression of the four Jak-family tyrosine kinases required for downstream signaling induced by the cytokine receptors expressed on T cells. The results from these experiments are shown in Figure. d) With the new information provided by the data shown above, name the most likely candidate molecule for the defect in Wm T cells, and explain your reasoning.

To generate a vaccine to pertussis toxin, a heat-killed preparation of Bordetella pertussis (the bacteria that produce pertussis toxin) is mixed with a purified preparation of the inactivated toxin protein. The mixture is then injected subcutaneously into mice. In an effort to enhance the antibody response to the toxin, a group of test mice is depleted of all their dendritic cells immediately prior to immunization. However, instead of enhancing the antibody response, the dendritic cell depletion nearly eliminated the anti-toxin antibody response because:

The entry of naive T cells from the blood into lymph nodes and mucosal lymphoid tissues occurs by a process that involves similar steps and similar adhesion molecules to the process by which leukocytes are recruited into sites of inflammation. Yet naive T cells do not enter tissues at sites of inflammation, but rather, home to lymphoid tissues. Which class of adhesion molecules direct the specific homing of naive T cells to lymphoid tissues?

Cytotoxic T cells are rapid killers of infected target cells. Within minutes of the interaction of a cytotoxic T cell with a target cell, the program of apoptosis in the target cell is initiated. This rapid activity is a consequence of:

Chimeric mice are generated where approximately 50% of the cells in the animal are genetically MHC class I-deficient. The other 50% are deficient for the herpes virus receptor, HVEM, but do express MHC class I molecules. When these mice are infected with herpesvirus by intraperitoneal injection, a robust virus-specific CD8 T cell response is detected at day 7 post-infection in the spleens of the infected mice. Which cells are presenting herpesvirus antigens to prime the CD8 T cell response, and how did they acquire the viral antigens? Microbe-induced TLR signaling in tissue-resident dendritic cells induces their migration to lymphoid organs and enhances antigen processing

Cytotoxic granules released from cytotoxic T cells contain proteins that enter target cells and induce apoptosis. Do any of the mechanisms of apoptosis induction by cytotoxic effector T cells rely on the protein APAF-1? If so, which pathway?

A T cell line growing in culture is subjected to a chemical mutagen, and individual mutant lines are derived from this population. The individual mutant cell lines are each screened for their ability to proliferate in response to stimulation with antibodies to the T-cell receptor plus CD28 (anti-CD3 + anti-CD28). In addition, the cells are treated with varying doses of added IL-2, and three days later, T cell proliferation is measured by ³H-thymidine incorporation (cpm). The data for one mutant line and the wild-type control are shown in Figure Q16). Figure Q16) The gene that is defective in this mutant T cell line most likely encodes:

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:

Unlike innate immune responses, adaptive immune responses are initiated in secondary lymphoid organs. However, the innate immune response to an infection in a tissue has a pivotal role in inducing T-cell responses in the nearest lymph node by activating tissue dendritic cells and inducing their migration to the lymph node.

Purified naive T cells isolated from a T-cell receptor transgenic mouse represent a homogeneous population of cells with specificity for a single known peptide:MHC complex. This specific peptide:MHC complex can be purified and formed into multivalent complexes, such as peptide:MHC tetramers. When the naive T cells are stimulated with their 'antigen' in the form of these peptide:MHC tetramers, the T cells show activation responses, including the up-regulation of genes that are induced within several hours after T-cell receptor stimulation. However, these activated T cells fail to undergo robust proliferation, and the majority of cells die after 3-4 days in culture. T cell proliferation and survival could be greatly augmented by addition of:

Naive T cells are isolated and left untreated or treated with 'compound X' for 1 hour. Following this, the T cells are incubated with a range of concentrations of a soluble form of ICAM-1 that has been conjugated to a fluorescent dye (soluble-ICAM-1-FITC). Fifteen minutes later, the cells are washed, and the relative amount of fluorescence bound to the cells is measured. The results of this assay are shown in Figure Q6). Figure Q6) The most likely identity of compound X is:

Effector caspases are activated downstream of both extrinsic and intrinsic pathways of apoptosis. Consequently, cells lacking one or more of these enzymes show defects in apoptosis. An alternative means of eliminating the activity of an effector caspase would be to:

Following their activation, naive CD4 T cells differentiate into one of several subsets of effector T cells. This developmental choice is determined by which specific cytokines the T cells are exposed to during their activation; in turn, the cytokines that are produced will reflect the nature of the infecting pathogen. In order for this system to be flexible enough to produce all five effector CD4 subsets (T_H1, T_H2, T_H17, T_FH, and iT_reg):