The Immune System

Vocabulary flashcards covering key terms and definitions from lecture notes on the immune system.

Immunology

The science concerned with the immune system and its responses to pathogens and foreign substances.

Primary lymphoid organs

Bone marrow and thymus; sites where T and B cells develop and become immunocompetent.

Secondary lymphoid organs

Lymph nodes, tonsils, and spleen; tissues where immunocompetent cells populate and respond to antigens.

Hematopoietic stem cells

Multipotent cells in bone marrow that give rise to all blood and immune cells.

Bone marrow

Soft, highly vascular tissue where hematopoiesis occurs; B cells mature there and long-lived plasma cells reside.

Thymus

Bilobed organ where T cells mature; has cortex and medulla; thymocytes mature and exit to blood.

Keratinocytes

Skin cells that form a physical barrier; express PRRs and produce antimicrobial compounds and cytokines.

Pattern-recognition receptors (PRRs)

Receptors that detect microbial components to trigger innate immune responses.

Toll-like receptors (TLRs)

A type of PRR that recognizes pathogen-associated patterns on or within cells.

NOD-like receptors (NLRs)

Intracellular PRRs that detect microbial components inside cells.

RIG-I-like receptors (RLRs)

Intracellular PRRs that detect viral RNA to initiate antiviral responses.

C-type lectins

Carbohydrate-binding receptors involved in pathogen recognition and immune signaling.

Langerhans cells

Epidermal dendritic cells that can promote Th17 responses against extracellular pathogens.

Dendritic cells

Highly mobile antigen-presenting cells concentrated in skin and mucosa; key in activating T cells.

Macrophages

Phagocytic antigen-presenting cells that ingest pathogens and present antigens to T cells.

Neutrophils

First-line phagocytes recruited to sites of infection during innate immunity.

Natural Killer (NK) cells

Large lymphocytes that kill infected or cancerous cells; release perforin and granzymes.

B cells

Lymphocytes that mature in bone marrow and produce antibodies; differentiate into plasma cells.

T cells

Lymphocytes that mature in the thymus and mediate adaptive cellular immunity.

Lymph nodes

Numerous organs that filter lymph and activate T and B cells; cortex and medulla with germinal centers.

Germinal center

Region within a lymph node follicle where B cells differentiate into plasma cells.

Spleen

Largest lymphatic organ with red pulp (erythrocyte-rich) and white pulp (lymphocytes/macrophages); filters blood.

Red pulp

Spleen region rich in erythrocytes; involved in removing aged blood cells.

White pulp

Spleen region rich in lymphocytes and macrophages; site of immune responses to blood-borne antigens.

MALT (mucosa-associated lymphoid tissue)

Lymphoid tissue associated with mucosal surfaces (GI, respiratory, GU tracts).

Peyer’s patches

Lymphoid follicles in the ileum; part of MALT; induce gut immune responses; interact with M cells.

M cells

Specialized antigen-transporting cells in mucosa that deliver antigens to underlying immune cells.

Tonsils

Lymphoid tissue guarding against ingested or inhaled pathogens; part of MALT; can become inflamed (tonsillitis).

IgA

Immunoglobulin A; antibody isotype predominant at mucosal surfaces; produced by mucosal B cells.

Mucosal immunity

Immune responses at mucosal surfaces, organized in MALT and lamina propria, often involving IgA.

Lamina propria

Connective tissue layer beneath mucosal epithelium housing immune cells.

Th17 responses

T helper 17 cell responses important for defense at mucosal surfaces and extracellular pathogens.

Thymocytes

Immature T cells developing in the thymus before becoming mature T cells.

Reticular cells

Branched stromal cells that form the supportive stroma of lymphoid organs.

Antigen

Substance that is recognized by the immune system and can elicit an immune response.

Antigen-presenting cells (APCs)

Cells (e.g., dendritic cells, macrophages) that display antigen fragments to T cells to activate them.

Antibody

Immunoglobulin produced by B cells that binds specifically to an antigen.

Inflammation

Innate defense involving leukocyte recruitment and mediator release to fight infection.

Complement system

A group of plasma proteins that assist in pathogen destruction as part of innate immunity.

Lymphadenitis

Swollen, painful lymph node in response to foreign antigen.

Lymphadenopathy

General term for diseases/abnormalities of lymph nodes.

Metastasis

Spread of cancer cells to nearby lymph nodes or other tissues via lymphatics.