Cells, Organs, and Tissues of the Immune System

Flashcards covering the cells, tissues, and organs of the immune system, including hematopoiesis, specific cell functions, and lymphoid organ classifications.

Immune System

A collection of cells, tissues, organs, molecules, and pathways that protect multicellular organisms against pathogens.

Innate immune cells

Cells that mount the first line of defense against pathogens, such as antigen-presenting cells that communicate infection to lymphoid cells.

Adaptive immune cells

Cells such as T and B cells that coordinate the adaptive response and generate memory cells to prevent future infections.

Hematopoietic stem cells (HSC)

Multipotent cells found in adult bone marrow with the capacity to regenerate (self-renew) and differentiate into diverse types of red and white blood cells.

Hematopoiesis

The development of all red and white blood cells from Hematopoietic Stem Cells.

Monocytes

Phagocytic cells that circulate in the blood and migrate to tissues to form macrophages.

Macrophages

Resident phagocytic cells in almost all tissues that locate, engulf, and destroy microbes, act as antigen-presenting cells for T lymphocytes, and secrete cytokines.

Alveolar macrophages

Specific fixed macrophages resident in the lungs.

Microglial cells

Specific fixed macrophages resident in the brain.

Dendritic cell

Star-shaped (tree-like) cells resident in most tissues that act as antigen-presenting cells to activate adaptive immunity and secrete cytokines.

Granulocytes

A group of cells including neutrophils, basophils, and eosinophils characterized by irregularly shaped nuclei with two to five lobes and granules that stain different colors.

Neutrophils

The first cells to arrive at sites of infection, making up $50\text{-}70\%$ of circulating white blood cells and possessing a multi-lobed nucleus.

Eosinophils

Phagocytic cells with bilobed nuclei involved in killing parasites and helminths, as well as regulating inflammation and allergy.

Basophils

Circulating cells containing histamine and leukotrienes that function in vasodilation, smooth muscle activation, and responses to parasitic worms.

Mast cells

Cells with indented nuclei localized in tissues like the skin that release histamine/leukotrienes for inflammation, allergy, and response to helminths.

Lymphocytes

Cells constituting $20\%\text{-}40\%$ of the body's white blood cells, broadly divided into B cells, T cells, and Natural killer cells.

B Lymphocyte

A lymphocyte distinguished by the B Cell Receptor (BCR) that functions in presenting antigen, producing antibodies, and secreting cytokines.

CD8+ T cytotoxic (Tc) cell

A T cell that monitors and eliminates cells displaying non-self-antigens complexed with MHC class I, using perforin and granzymes to induce apoptosis.

CD4+ T helper (TH) cells

Cells that help activate macrophages, cytotoxic T cells, B cells, and NK cells; categorized into types like Th1, Th2, Th17, and Tfh.

Regulatory T cell (TREG)

A type of T cell that functions to inhibit immune responses.

Natural killer (NK) cell

A non-phagocytic granular cell of the innate immune system that destroys infected or tumor cells lacking MHC I using perforin, granzymes, or ADCC.

Primary Lymphoid Organs

Sites of immune cell generation and maturation, specifically the Bone Marrow and the Thymus.

Secondary Lymphoid Organs

Sites where immune responses are initiated, including lymph nodes, the spleen, and MALT.

Bone Marrow

The origin of all immune cells and the specific site of B cell maturation.

Thymus

The site of T cell maturation and selection, ensuring T cells recognize self-MHC but not self-antigens.

Spleen

A secondary lymphoid organ that filters blood; the white pulp contains lymphocytes while the red pulp removes old red blood cells.

Mucosa-Associated Lymphoid Tissue (MALT)

A group of immune cells protecting mucosal surfaces, including the tonsils, Peyer's patches in the gut, and the appendix.