MCAT Biology : Immune Proteins and Signals

Study concepts, example questions & explanations for MCAT Biology

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Example Questions

Example Question #1 : Immune Proteins And Signals

In what part of the body do T cells undergo maturation?

Possible Answers:

Thymus

Tibia

Liver

Bone marrow

Spleen

Correct answer:

Thymus

Explanation:

T cells originate from hematopoietic stem cells in the bone marrow and migrate to the thymus where they undergo maturation.

Example Question #2 : Immune Proteins And Signals

The mechanisms of antibody-mediated antigen disposal occur in the what order?

Possible Answers:

Opsonization, agglutination, neutralization

Agglutination, neutralization, opsonization

Neutralization, agglutination, opsonization

Neutralization, opsonization, agglutination

Agglutination, opsonization, neutralization

Correct answer:

Neutralization, agglutination, opsonization

Explanation:

The mechanisms of antibody-mediated antigen disposal occur in the order of neutralization, agglutination, and opsonization. During the process of neutralization, antibodies block pathogenic activity. During agglutination, antibody molecules aggregate multiple pathogens. Finally, during opsonization phagocytes engulf pathogens bound to antibodies. 

Example Question #3 : Immune Proteins And Signals

Which toll-like receptor (TLR) recognizes single-stranded RNA?

Possible Answers:

TLR3

TLR4

TLR9

TLR5

TLR7

Correct answer:

TLR7

Explanation:

TLR7 recognizes single-stranded RNA while TLR9 recognizes DNA, TLR4 recognizes lipopolysaccharide from gram-negative bacteria, TLR5 recognizes flagellin, and TLR3 recognizes double-stranded RNA.

Example Question #4 : Immune Proteins And Signals

Major histocompatibility complex 1 (MHC-I) presents antigen to which T cell subclass?

Possible Answers:

CD4+ T cells

Neither CD4+ nor CD8+ T cells

A T cell subclass that is not listed in any of the other answer choices

Both CD4+ and CD8+ T cells

CD8+ T cells

Correct answer:

CD8+ T cells

Explanation:

MHC-I on antigen-presenting cells (such as dendritic cells and macrophages) presents antigen to CD8+ T cells. MHC-II presents antigen to CD4+ T cells.

Example Question #5 : Immune Proteins And Signals

Naive T cells need to be initially presented with antigen in order to be activated.  Which cell type is involved with this initial presentation?

Possible Answers:

Dendritic cells

Basophils

NK cells

Neutrophils

Platelets

Correct answer:

Dendritic cells

Explanation:

Out of all of the possible choices, only dendritic cells can process and present antigen to T cells. B cells and macrophages are other possible cell types that can be antigen-presenting cells.

Example Question #6 : Immune Proteins And Signals

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?

Possible Answers:

TLR5

TLR2

TLR4

TLR7

TLR9

Correct answer:

TLR7

Explanation:

TLR7 recognizes single-stranded RNA. TLR9 recognizes DNA, TLR4 recognizes lipopolysaccharide, TLR2 recognizes different bacterial components, TLR5 recognizes flagellin.

Example Question #7 : Immune Proteins And Signals

The complement system consists of plasma proteins that can directly or indirectly be activated by foreign pathogens. This leads to the induction of a signaling cascade of reactions that occurs on the surface of the pathogens, which leads to different effector functions including opsonization and neutralization. Deficiencies in different components of complement has been linked to an increased susceptibility to autoimmune diseases, including systemic lupus erythematosus (SLE).

Which of the following would be the most likely scenario regarding how a complement deficiency would result in an increased risk of developing autoimmunity?

Possible Answers:

Complement deficiency leads to an increase in inflammatory monocytes, which leads to a chronic inflammatory state.

Complement deficiency leads to decreased binding to self-antigens from apoptotic cells, resulting in an increased amount of self-antigen present, thus increasing the chances of encountering autoreactive lymphocytes.

Complement deficiency leads to increased killing of regulatory T cells, which allow autoreactive lymphocytes to escape apoptosis.

Complement deficiency leads to a decrease in the formation of antibody-antigen-complement immune complexes, resulting in decreased deposition on tissues.

Complement deficiency leads to increased apoptosis, which leads to a decrease in the presence of self-antigens, thus altering peripheral tolerance.

Correct answer:

Complement deficiency leads to decreased binding to self-antigens from apoptotic cells, resulting in an increased amount of self-antigen present, thus increasing the chances of encountering autoreactive lymphocytes.

Explanation:

The complement system is able to protect against immune responses to autoantigens through the elimination of lymphocytes that are reactive against self antigens. Complement proteins are able to coat self antigens from apoptotic cells and deliver them to developing B cells (through binding to the B cell's complement receptors) and enhancing negative selection. A defective complement system increases the amount of self-antigen present, which can lead to increased chances of binding to autoreactive lymphocytes.  

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