Immune System - MCAT Biology

Toll like receptors (TLR's) are pattern recognition receptors that recognize specific pathogen-associated molecular patterns (PAMP's) on different pathogens and induce an immune response against the foreign pathogen. Numerous immune cell types express TLR's, including antigen-presenting cells and natural killer cells. TLR's play a critical role in the recognition and induction of the immune response against viruses.

A person that has a decreased inherent ability to detect RNA viruses such as influenza and hepatitis would presumably have a defect in which specific TLR?

The common precursor for all blood and immune cells, including red blood cells and lymphocytes, is found in what part of the body?

Which types of leukocytes are granular?

Which is not a function of B cells?

Which of the following group of cells are of the myeloid lineage?

Which of the following statements is true?

Which of the following is NOT an antigen presenting cell?

Which of the following is not a true statement regarding germinal centers?

Which cytokine is typically associated with the T helper 1 (Th1) response?

What is the group of diseases called when a person's immune system loses its ability to recognize its own MHC proteins?

Which of the following class of immunoglobulins is normally responsible for the promotion of the allergy response?

Which of the following cell types is considered to be part of the innate immune response?

Systemic lupus erythematosus (SLE) is a chronic autoimmune disease characterized by the loss of tolerance to self antigens leading to the presence of high autoantibody titers. There are several underlying causes behind SLE, one of which is a dysregulation in the clearance of apoptotic cells, which can lead to secondary necrosis. This leads to the leakage of danger signals which contributes to the loss of peripheral tolerance and chronic inflammation.

A deficiency in the clearance of apoptotic cells can be attributed to which immune cell type?

Somatic hypermutation of B cell receptor (BCR) genes in immature, developing B lymphocytes generates numerous specificities that are useful against a specific foreign antigen, however the process generates many more specificities that are either low affinity or reactive against self-antigens. Tolerance mechanisms, which include apoptosis or anergy, are in place in the bone marrow to prevent these "non-useful" or "harmful" B cells from exiting. However, these checkpoints are not 100% accurate and numerous B cells with autoreactive BCR's leave and travel to secondary lymphoid tissues.

Tolerance checkpoints exist in secondary lymphoid tissues to purge the repertoire of low-affinity or autoreactive B cells. What is the tolerance checkpoint mechanism in the secondary lymphoid tissues referred to as?

Bone marrow chimeric mice are an invaluable tool used by immunologists to elucidate specific mechanisms of the immune response. The generation of these chimeras involve whole body irradiation to eliminate the mouse bone marrow followed by adoptive transfer of bone marrow from a donor mouse (usually transgenic).

One critical step in the successful generation of bone marrow chimeric mice involves the depletion of T cells from the donor bone marrow. Which of the following is reason for this necessary step?

Duchenne Muscular Dystrophy is an X-linked recessive genetic disorder, resulting in the loss of the dystrophin protein. In healthy muscle, dystrophin localizes to the sarcolemma and helps anchor the muscle fiber to the basal lamina. The loss of this protein results in progressive muscle weakness, and eventually death.

In the muscle fibers, the effects of the disease can be exacerbated by auto-immune interference. Weakness of the sarcolemma leads to damage and tears in the membrane. The body’s immune system recognizes the damage and attempts to repair it. However, since the damage exists as a chronic condition, leukocytes begin to present the damaged protein fragments as antigens, stimulating a targeted attack on the damaged parts of the muscle fiber. The attack causes inflammation, fibrosis, and necrosis, further weakening the muscle.

Studies have shown that despite the severe pathology of the muscle fibers, the innervation of the muscle is unaffected.

Which of the following does not play a key role in the adaptive immune response?

Sexually transmitted diseases are a common problem among young people in the United States. One of the more common diseases is caused by the bacterium Neisseria gonorrhoeae, which leads to inflammation and purulent discharge in the male and female reproductive tracts.

The bacterium has a number of systems to evade host defenses. Upon infection, it uses pili to adhere to host epithelium. The bacterium also uses an enzyme, gonococcal sialyltransferase, to transfer a sialyic acid residue to a gonococcal surface lipooligosaccharide (LOS). A depiction of this can be seen in Figure 1. The sialyic acid residue mimics the protective capsule found on other bacterial species.

Once infection is established, Neisseria preferentially infects columnar epithelial cells in the female reproductive tract, and leads to a loss of cilia on these cells. Damage to the reproductive tract can result in pelvic inflammatory disease, which can complicate pregnancies later in the life of the woman.

A key immune response to Neisseria in humans is the activity of macrophages. What is true of how macrophages combat infection?

Scientists use a process called Flourescent In-Situ Hybridization, or FISH, to study genetic disorders in humans. FISH is a technique that uses spectrographic analysis to determine the presence or absence, as well as the relative abundance, of genetic material in human cells.

To use FISH, scientists apply fluorescently-labeled bits of DNA of a known color, called probes, to samples of test DNA. These probes anneal to the sample DNA, and scientists can read the colors that result using laboratory equipment. One common use of FISH is to determine the presence of extra DNA in conditions of aneuploidy, a state in which a human cell has an abnormal number of chromosomes. Chromosomes are collections of DNA, the totality of which makes up a cell’s genome. Another typical use is in the study of cancer cells, where scientists use FISH labels to ascertain if genes have moved inappropriately in a cell’s genome.

Using red fluorescent tags, scientists label probe DNA for a gene known to be expressed more heavily in cancer cells than normal cells. They then label a probe for an immediately adjacent DNA sequence with a green fluorescent tag. Both probes are then added to three dishes, shown below. In dish 1 human bladder cells are incubated with the probes, in dish 2 human epithelial cells are incubated, and in dish 3 known non-cancerous cells are used. The relative luminescence observed in regions of interest in all dishes is shown below.

When the body recognizes that cells have become cancerous, it responds in part by mobilizing cell-mediated killing of cancer cells. What cells are most likely responsible for this killing?

Where do the T-cells of the immune system mature into functional T-cells?

Most scientists subscribe to the theory of endosymbiosis to explain the presence of mitochondria in eukaryotic cells. According to the theory of endosymbiosis, early pre-eukaryotic cells phagocytosed free living prokaryotes, but failed to digest them. As a result, these prokaryotes remained in residence in the pre-eukaryotes, and continued to generate energy. The host cells were able to use this energy to gain a selective advantage over their competitors, and eventually the energy-producing prokaryotes became mitochondria.

In many ways, mitochondria are different from other cellular organelles, and these differences puzzled scientists for many years. The theory of endosymbiosis concisely explains a number of these observations about mitochondria. Perhaps most of all, the theory explains why aerobic metabolism is entirely limited to this one organelle, while other kinds of metabolism are more distributed in the cellular cytosol.

Some version of phagocytosis was likely the initial event that introduced a free-living prokaryote into the host described in the passage. Which of the following cells is most commonly associated with phagocytosis?