Cells, Organs, and Microenvironments of the Immune System

A set of vocabulary-style flashcards covering key concepts, cells, organs, structures, and processes from the lecture notes.

Immune system

A network of cells, tissues, microenvironments, and molecules that defend against infection, eliminate abnormal cells, and maintain homeostasis.

Leukocytes

All white blood cells, including neutrophils, lymphocytes, monocytes, eosinophils, and basophils.

Neutrophils

The most abundant granulocyte; rapid responders that phagocytose and kill pathogens, key players in acute inflammation.

Lymphocytes

A group of white blood cells including B cells, T cells, and natural killer (NK) cells.

Monocytes

Circulate in blood and serve as precursors to macrophages and dendritic cells; highly phagocytic.

Eosinophils

Granulocytes that target parasites, contribute to antiviral defense, and participate in allergy and asthma.

Basophils

Rare granulocytes that release histamine and mediators; important in allergic inflammation.

Mast cells

Tissue-resident cells near vessels and epithelia that release histamine and cytokines; central to allergy and anaphylaxis.

Macrophages

Tissue-resident phagocytes that destroy pathogens and present antigens to T cells.

Dendritic cells

Potent antigen-presenting cells that capture antigens and migrate to lymph nodes to activate T cells.

Granulocytes

White blood cells with visible granules: neutrophils, eosinophils, and basophils.

Phagocytes

Cells that engulf and destroy pathogens, including macrophages, neutrophils, and dendritic cells.

B cells

Lymphocytes that produce antibodies and can differentiate into plasma cells and memory B cells.

T cells

Lymphocytes that coordinate immune responses (CD4+ helpers) and kill infected cells (CD8+ cytotoxic).

Natural killer (NK) cells

Innate lymphoid cells that destroy virus-infected and tumor cells without prior sensitization.

Innate lymphoid cells (ILCs)

Group including NK cells and ILC1–ILC3; part of the innate immune system with lymphoid characteristics.

Hematopoietic stem cells (HSCs)

Stem cells with self-renewal capacity that differentiate into all blood lineages; reside mainly in bone marrow.

Self-renewal

The ability of HSCs to make identical copies of themselves to maintain the stem cell pool.

Differentiation

Process by which stem cells become more specialized cell types (e.g., CMPs, CLPs).

Common Myeloid Progenitors (CMPs)

Progenitors giving rise to myeloid lineages: erythrocytes, monocytes, granulocytes, megakaryocytes, dendritic cells.

Common Lymphoid Progenitors (CLPs)

Progenitors giving rise to lymphoid lineages: B cells, T cells, NK cells, ILCs, and some dendritic cells.

Erythrocytes (RBCs)

Red blood cells derived from CMPs; transport oxygen and carbon dioxide.

Megakaryocytes

Large bone marrow cells that give rise to platelets; derived from CMPs.

Bone marrow

Primary site of hematopoiesis; where most immune cells develop and mature.

Thymus

Primary lymphoid organ where T cell maturation occurs after arrival as pro-thymocytes from bone marrow.

Primary lymphoid organs

Organs where lymphocytes develop and mature (bone marrow and thymus).

Secondary lymphoid organs

Organs where lymphocytes encounter antigens and become activated (lymph nodes, spleen, MALT).

Lymph nodes

Bean-shaped filters that trap antigens and organize immune responses; have cortex, paracortex, and medulla.

Spleen

Filters blood; contains red pulp (RBC/macrophages) and white pulp (PALS with T cells and follicles with B cells).

MALT (mucosa-associated lymphoid tissue)

Defense system at mucosal surfaces; includes BALT, NALT, GALT, and SALT.

GALT

Gut-associated lymphoid tissue; organized immune tissues in the gut, including Peyer’s patches and appendix.

Peyer’s patches

Lymphoid follicles in the ileum; contain B and T cells, dendritic cells, and M cells in the epithelium.

M cells

Specialized intestinal epithelial cells that sample lumen antigens and transport them to underlying immune cells.

Germinal centers

Sites within B cell follicles where B cells proliferate and differentiate during activation.

HEVs (high endothelial venules)

Blood vessels in LN paracortex that allow naive lymphocytes to enter from the bloodstream.

Afferent lymphatic vessels

Vessels that bring lymph, antigens, and dendritic cells into a lymph node.

Efferent lymphatic vessels

Vessels that carry activated lymphocytes, plasma cells, and antibodies out of the lymph node.

Cortex (thymus)

Outer T cell-poor or T cell-depleted zone in the thymus; site of early thymocyte development.

Medulla (thymus)

Inner region of the thymus with more mature thymocytes undergoing selection.

Positive selection

Thymic process in which thymocytes are tested for MHC recognition; occurs mainly in the cortex.

Negative selection

Thymic process removing self-reactive thymocytes; occurs mainly in the medulla.

DiGeorge syndrome

22q11.2 deletion leading to underdeveloped or absent thymus and severe T cell deficiency.

Thymic involution

Age-related shrinkage of the thymus; reduces thymic tissue and T cell output with aging.

PALS (periarteriolar lymphoid sheath)

T cell-rich zone in the spleen's white pulp surrounding central arteries.

Marginal zone

Spleen region between red and white pulp rich in macrophages and B cells; entry point for antigens.

IgA

Antibody isotype produced by B cells in GALT; secreted into the gut lumen to neutralize pathogens.

Positivity and selection in CD markers (CD4, CD8, CD19, CD3, etc.)

Cell surface proteins used to identify immune cell subsets and their functions (e.g., CD4: helper T cells; CD8: cytotoxic T cells; CD19/CD20: B cells).

Germinal center reaction

B cells proliferate and differentiate within germinal centers, leading to high-affinity antibodies and memory formation.

MALT subtypes (BALT, NALT, SALT)

Mucosa-associated lymphoid tissues in specific sites: bronchial/MALT, nasal/NALT, skin/SALT.