Immunology: Hematopoietic Lineages, Innate & Adaptive Immunity, and Key Immune Cells

What are the two main hematopoietic lineages?

Myeloid lineage and Lymphoid lineage.

Which lineage gives rise to innate immune cells like neutrophils and macrophages?

Myeloid lineage.

Which lineage gives rise to adaptive immune cells like B and T cells?

Lymphoid lineage.

What is the key difference between innate and adaptive immunity?

Innate is fast, nonspecific, and has no memory. Adaptive is slower, specific, and has memory.

What is the primary function of B cells?

Recognize antigen and differentiate into antibody-secreting plasma cells (humoral immunity).

What is the function of plasma cells?

They are the antibody-secreting effector form of B cells.

What are the two main types of T cells and their functions?

Cytotoxic T cells (kill infected cells) and Helper T cells (activate other immune cells).

What are the key functions of macrophages?

Phagocytosis, cytokine secretion, and antigen presentation.

Why are dendritic cells considered a link between innate and adaptive immunity?

They perform antigen uptake in tissues and present it to T cells in lymphoid organs.

What are monocytes?

Circulating precursors to macrophages and dendritic cells.

What are the primary functions of neutrophils?

First responders; phagocytosis, release of ROS (reactive oxygen species), and formation of NETs (neutrophil extracellular traps).

What is the role of basophils?

Release histamine; involved in allergic responses.

What is the role of mast cells?

Tissue-resident cells that release histamine; involved in allergic inflammation.

What is the role of eosinophils?

Defense against parasites; involved in allergy and asthma.

What are the primary lymphoid organs?

Bone marrow and Thymus.

What happens in the bone marrow?

Production of B and T cells; B cells mature here.

What happens in the thymus?

T cell maturation.

What are the secondary lymphoid organs?

Lymph nodes, Spleen, and MALT (Mucosa-Associated Lymphoid Tissue).

What is the function of lymph nodes?

Filter lymph; site of antigen presentation and T/B cell activation.

What is the function of the spleen?

Filters blood; clears blood-borne pathogens; site of antigen presentation.

What is MALT and what does it include?

Mucosa-Associated Lymphoid Tissue; includes GALT (gut) and BALT (bronchial).

How does MALT sample antigens?

Via specialized M cells.

What are the three types of barriers in the 1st line of defense?

Physical, Chemical, and Biological barriers.

Give examples of physical barriers.

Skin, mucosa, tight epithelial junctions.

Give examples of chemical barriers.

Low pH (stomach, vagina, skin), lysozyme, defensins.

What is a biological barrier?

Commensal microbiota that compete with pathogens.

What does PAMP stand for?

Pathogen-Associated Molecular Pattern.

What does PRR stand for?

Pattern Recognition Receptor.

What do PRRs recognize?

PAMPs.

Name four types of PRRs.

Toll-like receptors (TLRs), Lectins, Scavenger receptors, Cytosolic receptors (e.g., RIG-I, NOD-like).

What is the function of opsonin receptors?

To recognize complement proteins or antibodies bound to microbes (opsonization).

Describe the four steps of phagocytosis.

1. PRR binding. 2. Engulfment into phagosome. 3. Fusion with lysosome. 4. Destruction of pathogen.

What are key cytokines released by macrophages?

IL-1, TNF-α, IL-6, IL-12, CXCL8.

How do NK cells kill target cells?

By releasing perforin and granzymes.

What are ILCs and what do they do?

Innate Lymphoid Cells; they secrete cytokines to activate other immune cells.

What are the three main systemic responses to infection?

Inflammation, Fever, and Complement activation.

What are the four cardinal signs of inflammation?

Redness, Heat, Swelling, Pain (caused by vasodilation, permeability, and leukocyte recruitment).

What causes a fever?

Cytokines (like IL-1, IL-6, TNF-α) acting on the hypothalamus.

What are the three main outcomes of complement activation?

Opsonization, Inflammation, and Direct Lysis (MAC attack).