Mechanisms of Immunity in Animals

Active Immunity

durable immune protection developed when the body's immune system produces specific antibodies and memory cells after pathogen exposure or vaccination

Adaptive Immunity

immune response involving B and T cells that develops memory for rapid defense against known antigens

Anatomical Barriers

physical defenses such as intact skin and mucous membranes that prevent infection

Antibody

Y-shaped immunoglobulins that bind to antigens to neutralize or mark them

Antigen

foreign substances that bind antibodies or activate immune cells

Antigen Presentation

display of processed antigens on MHC molecules to activate T cells

B Lymphocytes/B Cells

bone marrow–derived lymphocytes that become plasma or memory cells

B-Cell Activation

triggered by antigen binding and T cell help, leading to plasma cell development

Basophil

histamine-releasing granulocyte in hypersensitivity reactions

Bone Marrow

primary site for blood cell production and immune cell origin

Cell-Mediated Immunity

immune defense via cytotoxic and helper T cells, independent of antibodies

Chemotaxis

directed migration of immune cells along chemical gradients

Colostrum

newborn's early nutrient source containing protective immunoglobulins

Complement System

cascade of proteins that enhance phagocytosis and cell lysis

Complete Blood Count/CBC

measures red cells, white cells, and platelets to evaluate immune and overall health

Cytology

analysis of cell shape and structure for disease detection

Cytotoxic

describes immune actions or agents that destroy cells directly

Cytotoxic T Cells/CD8+

lymphocytes that destroy infected or abnormal cells via toxic granules

Dendritic Cell

antigen-presenting cells that process and present antigens to T cells

Eosinophil

granulocyte involved in parasitic defense and allergic reactions

Fever

hypothalamic-mediated temperature increase that enhances immunity and limits pathogen growth

Helper T Cell/CD4+

CD4+ lymphocytes that activate B cells and macrophages

Humoral Immunity

circulating antibodies target extracellular pathogens

Hypersensitivity

exaggerated immune responses that can damage tissues

Immune Memory

memory B and T cells enable faster, stronger responses upon re-exposure

Immune System

integrated cells, tissues, and molecules that recognize and defend against pathogens

Immunity

resistance to disease via innate or acquired mechanisms

Immunocompetent

capable of mounting effective immune responses and memory formation

Immunocompromised

weakened immune systemeduced immune function from disease, drugs, or age

Immunoglobulin

family of antibody proteins with distinct immune roles

Innate Immunity

non-specific barriers and cells that provide immediate protection

Left Shift

increased immature neutrophils indicating acute infection

Lymph Nodes

lymphoid organs that filter lymph and initiate immune responses

Lymphadenopathy

abnormal node enlargement due to infection, inflammation, or neoplasia

Lymphatic System

vessels and nodes that circulate lymph and house immune cells

Lymphocyte

B, T, and NK cells mediating adaptive responses

Macrophage

phagocytic cells that present antigens and coordinate inflammation

Mucous Membranes

epithelial surfaces with mucus and antimicrobial substances

Natural Killer (NK) Cell

innate lymphocytes recognizing stressed or abnormal cells without prior sensitization

Normal Flora

commensals that compete with pathogens and support immune function

Opsonization

antibody or complement coating that enhances phagocytosis

Pathogen

infectious agent capable of causing disease in a host

Phagocytosis

engulfment and digestion of particles by immune cells

Plasma Cell

differentiated B lymphocytes specialized for antibody secretion

Regulatory T Cell

T cells suppressing immune responses for homeostasis

Skin Integrity

functional epidermis and dermis preventing pathogen entry and fluid loss

Spleen

secondary lymphoid organ involved in blood filtration and immune surveillance

Splenomegaly

abnormal enlargement due to immune activity, congestion, or disease

T Lymphocytes/T Cells

thymus-matured lymphocytes with helper, cytotoxic, and regulatory roles

T-Cell Activation

antigen recognition and cytokine-mediated transformation into effector cells

Three Lines of Defense

physical/chemical barriers, innate responses, and adaptive immunity working together

Tonsils

aggregated lymphoid nodules sampling antigens and initiating local immune responses

White Blood Cells/Leukocytes

nucleated cells including granulocytes, lymphocytes, and monocytes that mediate immune responses