All questions of Immune System for MCAT Exam

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.

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.