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All questions of Immune System for MCAT Exam

Recognition of self vs. non-self by the adaptive immune system in humans is accomplished in which of the following ways?
  • a)
    Exposure of B cells to the body’s own antigens in the thymus
  • b)
    Exposure of B cells to the body’s own antigens in the bursa of Fabricius
  • c)
    Exposure of T cells to the body’s own antigens in the bursa of Fabricius
  • d)
    Exposure of T cells to the body’s own antigens in the thymus
Correct answer is option 'D'. Can you explain this answer?

Orion Classes answered
Recognition of self vs. non-self by the adaptive immune system is primarily achieved through the process of T cell education or maturation in the thymus. The thymus is a specialized organ located in the chest where T cells develop and differentiate. During this process, T cells are exposed to a wide range of self-antigens presented by specialized cells within the thymus called antigen-presenting cells (APCs). T cells that recognize self-antigens with high affinity are eliminated through a process called negative selection, ensuring that the mature T cells do not react against the body's own tissues. This process helps establish self-tolerance and prevents autoimmune reactions. B cells, on the other hand, mature in the bone marrow and are not directly involved in recognizing self vs. non-self during their development.

Monocytes move from the systemic circulatory system into general connective tissues, where they differentiate into what phagocytic cell type?
  • a)
    Macrophage
  • b)
    T cell
  • c)
    B cell
  • d)
    Neutrophil
Correct answer is option 'A'. Can you explain this answer?

Orion Classes answered
Monocytes are a type of white blood cell that circulate in the bloodstream. When they migrate from the systemic circulatory system into the general connective tissues, they differentiate into macrophages. Macrophages are highly phagocytic cells that play a key role in the immune response by engulfing and digesting pathogens, cellular debris, and other foreign substances. They are important components of the innate immune system.

Myelogenous leukemias are caused by the cancerous production of innate (non-specific) immune system cells: in which tissue is such production most likely to occur?
  • a)
    Bone marrow
  • b)
    Thymus
  • c)
    Spleen
  • d)
    Lymph nodes
Correct answer is option 'A'. Can you explain this answer?

Matthew Turner answered
Understanding Myelogenous Leukemias
Myelogenous leukemias are a type of cancer that arises from the uncontrolled proliferation of myeloid cells, which are part of the innate immune system. To understand why the bone marrow is the most likely site for this production, let’s delve into the roles of different tissues involved in hematopoiesis.
Bone Marrow: The Primary Site of Hematopoiesis
- The bone marrow is the primary site where all blood cells, including myeloid and lymphoid lineages, are produced.
- Myelogenous leukemias specifically involve myeloid cells, which include granulocytes, monocytes, erythrocytes, and platelets, all generated from hematopoietic stem cells in the bone marrow.
- In cases of myelogenous leukemia, mutations occur in the DNA of these progenitor cells, leading to the uncontrolled growth of myeloid lineage cells.
Other Tissues: Thymus, Spleen, and Lymph Nodes
- The thymus primarily functions in the maturation of T lymphocytes, not myeloid cells, making it irrelevant for myelogenous leukemias.
- The spleen and lymph nodes are involved in filtering blood and lymph, respectively, and play roles in the adaptive immune response, but they are not the sites of initial blood cell production.
- While these organs can be affected by leukemic cells as the disease progresses, they do not produce myelogenous leukemias.
Conclusion
In summary, the bone marrow is indeed the correct answer as it is the primary site where myeloid cells are produced and where the malignant transformation leading to myelogenous leukemias occurs.

Which of the following cell types of the innate immune system does not perform phagocytosis?
  • a)
    Neutrophils
  • b)
    Basophils
  • c)
    Macrophages
  • d)
    Eosinophils
Correct answer is option 'B'. Can you explain this answer?

Zoe Brooks answered
Overview of Innate Immune Cell Types
The innate immune system is the body's first line of defense against pathogens. It includes various cell types that perform different functions, notably phagocytosis, which is the process of engulfing and digesting harmful entities like bacteria and dead cells.
Cell Types Discussed
- Neutrophils:
- These are the most abundant white blood cells in the immune system.
- They are highly effective at phagocytosing bacteria and fungi, serving as the first responders to sites of infection.
- Macrophages:
- Derived from monocytes, macrophages are large phagocytic cells.
- They play a crucial role in engulfing pathogens, dead cells, and debris, and also help activate other immune cells.
- Eosinophils:
- These cells are primarily involved in combating multicellular parasites and certain infections.
- They can also perform phagocytosis, although it's not their primary function.
- Basophils:
- Basophils are the least common type of granulocytes and do not perform phagocytosis.
- They primarily release histamines and other mediators during allergic reactions and inflammatory responses, aiding in vasodilation and increasing blood flow to affected tissues.
Conclusion
In summary, basophils (option B) are the correct answer as they do not engage in phagocytosis. Instead, they release substances that play a role in allergic reactions and inflammation, differentiating them from neutrophils, macrophages, and eosinophils, which are all capable of phagocytosis.

Which type of immune response is the first line of defense against pathogens and does not require prior exposure to the pathogen?
  • a)
    Innate immunity
  • b)
    Adaptive immunity
  • c)
    Active immunity
  • d)
    Passive immunity
Correct answer is option 'A'. Can you explain this answer?

Orion Classes answered
Innate immunity is the nonspecific defense mechanism that is present at birth. It provides immediate protection against a wide range of pathogens and does not require prior exposure to the pathogen.

Which type of immunity is temporary and acquired through the transfer of antibodies from another individual?
  • a)
    Innate immunity
  • b)
    Adaptive immunity
  • c)
    Active immunity
  • d)
    Passive immunity
Correct answer is option 'D'. Can you explain this answer?

Orion Classes answered
Passive immunity is temporary and acquired through the transfer of pre-formed antibodies from another individual or through maternal transfer to a fetus or newborn. It provides immediate protection but does not result in long-term immunity.

Which cells are responsible for phagocytosis and engulfing pathogens or cellular debris?
  • a)
    B cells
  • b)
    T cells
  • c)
    Macrophages
  • d)
    Natural killer cells
Correct answer is option 'C'. Can you explain this answer?

Orion Classes answered
Macrophages are specialized immune cells that engulf and digest pathogens, cellular debris, and other foreign substances through a process called phagocytosis. They are important components of the innate immune response.

Which portion of an antibody provides antigen-binding sites?
  • a)
    Light chain
  • b)
    Constant portion
  • c)
    Heavy chain
  • d)
    Variable portion
Correct answer is option 'D'. Can you explain this answer?

Orion Classes answered
The variable portion of an antibody, which is part of the heavy chain and the light chain, is responsible for providing antigen-binding sites. The variable regions contain hypervariable regions, also known as complementarity-determining regions (CDRs), which directly interact with antigens. The CDRs exhibit high variability in their amino acid sequences, allowing antibodies to recognize and bind to a wide range of antigens. The constant portion of the antibody, on the other hand, is responsible for other functions such as effector mechanisms and determining the antibody's class or isotype.

Humoral immunity is a type of adaptive immunity that results in the circulation of which of the following throughout the blood?
  • a)
    Antigens
  • b)
    Macrophages
  • c)
    Natural killer cells
  • d)
    Antibodies
Correct answer is option 'D'. Can you explain this answer?

Orion Classes answered
Humoral immunity refers to the component of adaptive immunity that involves the production and circulation of antibodies in the blood. Antibodies, also known as immunoglobulins, are proteins produced by B cells (a type of lymphocyte) in response to the presence of specific antigens. Once produced, antibodies are released into the bloodstream and other body fluids, where they can recognize and bind to specific antigens. This binding triggers various immune responses, including neutralization of pathogens, activation of complement system, and recruitment of other immune cells to eliminate the antigen. The circulation of antibodies in the blood allows them to reach various tissues and organs, providing a systemic defense against pathogens and foreign substances.

Which type of immune cells are responsible for producing antibodies?
  • a)
    B cells
  • b)
    T cells
  • c)
    Macrophages
  • d)
    Natural killer cells
Correct answer is option 'B'. Can you explain this answer?

Orion Classes answered
B cells are immune cells that produce antibodies. When activated by antigens, B cells differentiate into plasma cells, which secrete large amounts of antibodies specific to the encountered antigen.

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