Exam 11: Integrated Dynamics of Innate and Adaptive Immunity

In the cases of some infections, such as mice infected with adenovirus, the generation of effector cytotoxic CD8 T cell responses needed to clear the infection is dependent on the antigen-presenting dendritic cells receiving stimulation through the CD40 receptor on their surface, a process known as dendritic cell 'licensing'. In this infection system, the dendritic cell would likely receive CD40 receptor stimulation from:

Infections of intracellular pathogens (e.g., mycobacteria, listeria, toxoplasma, viruses, etc.) cause a rise in the numbers of monocytes in the blood, a symptom known as monocytosis. In the cases of these infections, monocytosis is likely caused by:

Hyper-IgE syndrome, also known as Job’s syndrome, is an immunodeficiency disease resulting from the lack of function of a single gene (gene ‘X’). Patients with this disease are highly susceptible to infections with extracellular bacteria and fungi, most frequently including Staphylococcus aureus infections and Candida albicans infections in the skin. Analysis of the various immune cell compartments indicates that these patients have normal numbers of each cell lineage (i.e., CD4 and CD8 T cells, B cells, monocytes, dendritic cells, NK cells, granulocytes, etc.), and normal levels of IgG, IgA, and IgM antibodies, but higher than normal levels of IgE. a) Given this information, name a likely component of the immune response that could be impaired in these patients. To investigate the immune mechanism impaired in these patients, a mouse model of this gene deficiency was generated. Conditional knockout mouse lines were generated in which gene X was knocked out in either the T cells, the B cells, or the myeloid cells of the mouse. For each conditional knockout line, mice were challenged with Candida albicans, and the ability to clear the infection was assessed. In mice, infection of the oral cavity with Candida albicans has been shown to be a valid model for mucosal Candida albicans infections in humans. After infection, the response was assessed by measuring fungal burden (CFU/g tissue) on the tongue. The resulting data are shown in Figure b) Based on these data, what is the most likely immune function impaired in the Gene X-deficient patients? Histological examination of tongue sections from Candida albicans infected mice were examined, and the numbers of infiltrating leukocytes (white blood cells) were quantified in each microscopic field of each section, and the results are shown in Figure c) Do these data support or refute your hypothesis stated in response to question (b)? Why or why not? To examine the details of T cell responses when Gene X is absent from the T cells, a series of in vitro experiments were performed. CD4 T cells were isolated from wild type mice and from T cell-deleted Gene X knockout mice, and were stimulated in vitro with a combination of anti-CD3 and anti-CD28 antibodies to activate the T cells. In addition, each culture was supplemented with one of the following cytokine conditions: (1) IFN- $\gamma$ plus IL-12; (2) IL-4; or (3) IL-6, TGF- $\beta$ , IL-1 plus IL-23. After four days, the cells were examined for the expression of transcription factors by RT-PCR, as shown in Figure. Note that Gene X does not encode T-bet, GATA-3, or ROR $\gamma$ t. Instead, these data indicated impaired responses of Gene X-deficient T cells to the cytokines used in these in vitro culture experiments. d) Based on these data, name three candidate genes that could be Gene X.

Nitric oxide and superoxide radicals are toxic compounds that induce substantial DNA damage. When released by activated M1 macrophages, these compounds cause damage to microbial pathogens and may also cause damage to host cells in the vicinity.

In addition to producing distinct innate responses locally at the site of infection, the different cytokines produced during type I, type 2, or type 3 immune responses also induce distinct adaptive immune responses that are tailored to the eradication of the three different classes of pathogens. One example is the production of different classes of antibodies during type I, type 2, or type 3 responses. Which step during the induction of the adaptive immune response is the key to generating and coordinating the three different immune modules?

Helicobacter pylori is a human gastrointestinal (GI) pathogen that can lead to a state of chronic GI inflammation in some individuals, and has been linked to gastric ulcers and other diseases. Studies have shown that human mucosal gastric biopsies of infected individuals have dendritic cells producing IL-23, and that human monocytes isolated and cultured from healthy individuals produce IL-23, but not IL-12, in response to stimulation with live H. pylori. Given these findings, which of the following responses would be enhanced in the GI tract of H. pylori-infected individuals compared to uninfected individuals?

Synthesis question: Leishmania parasites are intracellular protozoa that causes skin sores, and in some individuals, infections that spread systemically and cause damage to internal organs. In mice, different strains of inbred mice have varying responses to the Leishmania parasite Leishmania major. Whereas C57BL/6 mice develop self-healing skin lesions following infection, Balb/c mice develop non-healing lesions and ultimately succumb to systemic, fatal disease. An example of such data is shown in Figure Q28)A. For these studies, mice were infected with 2 $\times$ 10⁶ L. major promastigotes in the footpad, and the sizes of skin lesions and the numbers of parasites per lesion were measured at the indicated times post-infection. An example of the cytokine data from L. major infected mice is shown in Figure Q28)B. At the indicated times the percentages of CD4 T cells in the draining lymph node producing IFN- $\gamma$ versus IL-4 following stimulation with L. major antigens were measured by intracellular cytokine staining. on T_H1 effector T cells, CD8 effector T cells, and NK cells. These chemokines are normally not detectable in healthy tissues, but are strongly up-regulated during infection, injury or inflammation, in response to IFN- $\gamma$ production in the tissue. d) How might this information help explain the divergent ability of C57BL/6 versus Balb/c mice to accumulate increasing numbers of effector T cells into the L. major lesions over the long timecourse shown in the data above?

The generation of optimal CD8 T cell memory following a primary infection requires CD4 T cell help for the responding CD8 T cells. This requirement for CD4 T cell help would not be completely replaced by supplying high levels of the cytokine IL-2 during the primary CD8 T cell response.

Leprosy is a disease caused by the intracellular bacterium Mycobacterium leprae, which infects macrophages and replicates in their phagosomes. Human patients with leprosy have a persistent infection of the mycobacteria, as their immune systems are unable to complete eradicate the pathogen. Furthermore, two different forms of the disease have been identified. Some patients have many skin lesions containing a large number of bacteria with little inflammatory response. This is the very disfiguring form of the disease, and is known as lepromatous leprosy. In other patients, few skin lesions and only occasional bacteria are observed, and the skin lesions are accompanied by a robust inflammatory response. These patients have the form of the disease known as tuberculoid leprosy. If one examined a skin biopsy from a patient with tuberculoid leprosy, one would expect to see:

Immunological memory in humans has been examined by assessing responses in individuals who were given the vaccinia virus to induce immunity against smallpox. Antiviral CD4 and CD8 T cell responses could be detected many years after the vaccinia immunization, but declined with an estimated half-time of about 10 years. In contrast, antiviral antibody responses were maintained at a relatively constant level, with a barely detectable decline over decades. The persistence of antiviral antibodies for years after immunization is likely due to:

One of the first studies using peptide:MHC class I tetramers to measure the frequencies of virus-specific CD8 T cells in an acute virus infection in mice demonstrated the remarkable finding that more than 50% of all the CD8 T cells in the mouse were virus-specific at the peak of the response (day 8 post-infection). This study used the virus lymphocytic choriomeningitis virus (LCMV). One peptide:MHC tetramer used in this study, H-2-D^b loaded with the LCMV nucleoprotein peptide NP_396-404, bound to ~20% of the CD8 T cells in the spleen at day 8 post-infection. Why did this tetramer only stain ~20% of the CD8 T cells if more than half of the CD8 cells in the spleen were virus-specific?

IL-23 is a cytokine made by macrophages and dendritic cells in response to extracellular bacterial and fungal infections. Mice with a genetic defect in the production of IL-23 are highly susceptible to the gastrointestinal bacterial pathogen, Citrobacter rodentium. Thus, unlike wild-type mice which clear the infection, mice that fail to produce IL-23 succumb to the bacteria and die 1-2 weeks post-infection. Yet, this cytokine does not directly act on the bacteria nor does it function to recruit the granulocytes that are needed to eliminate the pathogen. Instead, IL-23:

The kinetics of a typical CD8 T cell response to an acute virus infection in mice is shown in Figure . and starting at ~day 10 post-infection, the majority of the virus-specific CD8 T cells die. The death of these virus-specific CD8 T cells is caused by:

Individuals with the HIV-induced immunodeficiency disease AIDS have a progressive loss in the number of CD4 T cells in their bodies. These patients have a greatly increased rate of life-threatening disease caused by the inability of their immune system to control infections of the intracellular bacterium, Mycobacterium tuberculosis (Mtb). Mtb infects macrophages and then replicates in the cell's phagosomes. The most important immune mechanism lacking in these patients that leads to their increased susceptibility to Mtb is a defect in:

In some infectious diseases, antibodies specific for the pathogen are not essential for clearing a primary infection with that pathogen, but are essential in preventing re-infection by the same pathogen. This protective role of pathogen-specific antibodies is not useful for any clinical applications.

While innate immune responses to all types of infections induce local inflammatory responses due to activation of blood vessel endothelial cells, some components of the innate response differ depending on the nature of the pathogen. In the case of intracellular bacterial or protozoan infections, tissue-resident dendritic cells and macrophages produce a cytokine that stimulates ILC cells to produce:

Inflammatory bowel disease (colitis) is a CD4 T-cell mediated disease that can be transferred to naive mice by administration of effector CD4 T cells that home to the gastrointestinal tract and induce inflammation. Simultaneous administration of neutralizing antibodies to IL-12p40 can prevent the disease, as can neutralizing antibodies to IL-23p19. Disease symptoms can be exacerbated by administration of IL-23, but not of IL-12. These data strongly suggest that:

It is well documented that antibody affinities for an immunizing antigen continue to increase upon successive rounds of immunization (i.e., secondary, tertiary, etc.). This is due to the fact that:

In response to an intracellular bacterial or viral infection, effector T_H1 cells, macrophages, NK cells, and CD8 cytotoxic effector cells are all recruited to the site of infection. The coordinated recruitment of all of these cell types is orchestrated by:

Vaccinia virus, used to immunize individuals against smallpox, has a long history of well-documented safe use in humans. Due to the eradication of smallpox, immunizations with vaccinia virus were halted, and babies born after 1970 no longer received this vaccine. This has led to the proposal to engineer vaccinia virus to express proteins derived from other human pathogens for which there are no current vaccines. For instance, the gene encoding the F protein of the respiratory syncytial virus (RSV) has been inserted into vaccinia virus (VaccV-F), and has been tested for its ability to induce anti-F protein antibody responses following immunization.strain if they were born before versus after 1970?