Immunology Glossary

A substance added to a vaccine to enhance the immune response to the antigen. Adjuvants work by activating innate immune pathways, promoting antigen uptake by dendritic cells, and creating a depot effect that prolongs antigen exposure. Common adjuvants include aluminum salts and MF59.

A state of functional unresponsiveness in lymphocytes that occurs when a T cell or B cell recognizes its antigen but fails to receive adequate co-stimulatory signals. Anergy serves as a peripheral tolerance mechanism to prevent autoimmune responses.

Any molecule capable of being recognized by the adaptive immune system, specifically by antibodies or T cell receptors. Antigens are typically proteins, polysaccharides, or lipids found on pathogens, foreign cells, or abnormal self-cells.

A cell that displays antigen-MHC complexes on its surface for recognition by T cells. Professional APCs include dendritic cells, macrophages, and B cells, all of which express MHC class II and co-stimulatory molecules necessary for T cell activation.

Programmed cell death, a controlled process of cellular self-destruction essential for eliminating infected cells, autoreactive lymphocytes, and cells that are no longer needed. Unlike necrosis, apoptosis does not trigger inflammation.

A pathological condition in which the immune system mounts an immune response against the body's own tissues, resulting from a breakdown in immune tolerance. Can be organ-specific (e.g., Type 1 diabetes) or systemic (e.g., systemic lupus erythematosus).

A subfamily of small cytokines that function primarily as chemoattractants, directing the migration of immune cells along concentration gradients to sites of infection, inflammation, or lymphoid organs. Examples include CXCL8 (IL-8, neutrophil attractant) and CCL2 (monocyte attractant).

A cascade of over 30 serum proteins that complement the activity of antibodies in destroying pathogens. Functions include opsonization (C3b), inflammation (C3a, C5a anaphylatoxins), and direct pathogen lysis (membrane attack complex, C5b-C9).

A broad category of small signaling proteins secreted by immune cells that mediate and regulate immunity, inflammation, and hematopoiesis. Major families include interleukins, interferons, tumor necrosis factors, and chemokines.

The specific portion of an antigen molecule that is recognized and bound by an antibody or T cell receptor. A single antigen may contain multiple epitopes, each capable of binding a different antibody or T cell receptor.

A transient microanatomical structure that forms within B cell follicles of secondary lymphoid organs during T cell-dependent immune responses. Germinal centers are the sites of B cell proliferation, somatic hypermutation, affinity maturation, class switching, and memory B cell generation.

The process of blood cell formation, occurring primarily in the bone marrow. All blood cells, including immune cells, arise from pluripotent hematopoietic stem cells that differentiate into myeloid and lymphoid lineages under the influence of specific growth factors and cytokines.

A state in which the immune system's ability to fight infectious disease is compromised or absent. Primary immunodeficiencies are inherited genetic defects, while secondary (acquired) immunodeficiencies result from external factors such as HIV infection, malnutrition, or immunosuppressive drugs.

Another term for antibody. A glycoprotein produced by B cells and plasma cells that specifically binds antigens. Each immunoglobulin molecule consists of two identical heavy chains and two identical light chains, forming a characteristic Y-shape with variable (antigen-binding) and constant (effector function) regions.

A category of medical treatments that harness or modulate the immune system to treat disease, particularly cancer. Approaches include checkpoint inhibitors, CAR-T cell therapy, monoclonal antibodies, cancer vaccines, and cytokine therapy.

A protective response to infection or tissue injury characterized by redness, heat, swelling, pain, and loss of function. Mediated by cytokines, prostaglandins, and histamine, inflammation recruits immune cells and plasma proteins to the site of damage.

A family of cytokines with antiviral and immunomodulatory properties. Type I interferons (IFN-alpha, IFN-beta) are produced by virus-infected cells and induce antiviral states in neighboring cells. Type II interferon (IFN-gamma) is produced by T cells and NK cells and activates macrophages.

A type of white blood cell central to the adaptive immune system. The three main types are T lymphocytes (cell-mediated immunity), B lymphocytes (antibody production), and natural killer cells (innate lymphoid cells).

A large phagocytic cell derived from circulating monocytes that resides in tissues throughout the body. Macrophages engulf and destroy pathogens, present antigens to T cells, and secrete cytokines that regulate inflammation and tissue repair.

A large genetic locus encoding cell surface glycoproteins essential for antigen presentation to T cells. In humans, MHC is known as HLA (human leukocyte antigen). MHC genes are the most polymorphic in the human genome, contributing to individual variation in immune responses.

The immune defense system operating at mucosal surfaces (respiratory, gastrointestinal, urogenital tracts) that represent the largest interface between the body and the external environment. Key features include secretory IgA production, mucus-associated lymphoid tissue (MALT), and specialized epithelial barrier functions.

A molecule (typically IgG antibody or complement fragment C3b) that binds to the surface of a pathogen and enhances its recognition and phagocytosis by phagocytic cells bearing the corresponding Fc or complement receptors.

Immunity conferred by the transfer of preformed antibodies from one individual to another, rather than by the recipient's own immune response. Natural passive immunity occurs via maternal antibodies (IgG across placenta, IgA in breast milk). Artificial passive immunity involves injection of therapeutic antibodies or antiserum.

The process by which cells such as macrophages and neutrophils engulf and internalize pathogens, dead cells, or debris into intracellular vesicles called phagosomes, which then fuse with lysosomes for enzymatic degradation.

A primary lymphoid organ located in the anterior mediastinum where T cell precursors from the bone marrow undergo maturation, positive selection, and negative selection. The thymus is most active during childhood and gradually involutes with age (thymic involution).