Adaptive Immunity – Humoral Immunity & Antibody Vocabulary

Vocabulary flashcards covering antibody structure, classes, functions, B-cell biology, and humoral immune responses.

Adaptive Immunity

Specific immune defense system that develops after exposure to antigens, involving humoral and cell-mediated responses.

Humoral Immunity

Branch of adaptive immunity mediated by antibodies produced by B lymphocytes.

Antigen

Any foreign molecule that can be specifically recognized and bound by an antibody.

Antibody (Immunoglobulin)

Y-shaped protein produced in response to an antigen and capable of specifically binding to that antigen.

Monomer (in antibodies)

Single Y-shaped antibody unit with two antigen-binding sites.

Valence

Number of antigen-binding sites on an antibody molecule.

Variable (V) Region

Portion of both heavy and light chains that forms the antigen-binding site and differs among antibodies.

Constant (C) Region

Portion of the antibody chains that is identical within a class and determines the antibody’s functional class.

Fc Region

Stem of the antibody heavy chains that can bind complement or attach to host cell receptors; basis for class differentiation.

Epitope

Specific part of an antigen recognized and bound by an antibody or B-cell receptor.

IgG

Most abundant serum antibody (≈80%); crosses placenta, activates complement, enhances phagocytosis, neutralizes toxins; monomer.

IgM

First antibody produced in primary response; effective complement activator and agglutinator; pentamer with valence 10.

IgA

Antibody found in secretions (tears, saliva, mucus, milk); protects mucosal surfaces; dimer in secretions, monomer in serum.

IgD

Minor serum antibody found on B-cell surfaces acting as B-cell receptor; function in serum unclear; monomer.

IgE

Antibody bound to mast cells & basophils; responsible for allergic reactions and defense against parasitic worms; monomer.

Neutralization

Antibody function in which toxins or microbes are blocked from attaching to host cells.

Agglutination

Clumping of antigens by antibodies, facilitating phagocytosis and clearance.

Opsonization

Coating of pathogens by antibodies to enhance recognition and ingestion by phagocytes.

Complement Activation

Triggering of the complement cascade by antibodies, leading to lysis of pathogens.

Antibody-Dependent Cell-Mediated Cytotoxicity (ADCC)

Killing of antibody-coated target cells by immune cells such as NK cells.

B Cell (B Lymphocyte)

White blood cell that matures in bone marrow, expresses B-cell receptors, and differentiates into plasma or memory cells.

B-Cell Receptor (BCR)

Membrane-bound antibody on a B cell that binds a specific epitope.

Plasma Cell

Effector B cell that secretes large quantities of soluble antibodies.

Memory B Cell

Long-lived B cell formed after activation that enables rapid, enhanced response on re-exposure to the same antigen.

Naïve Lymphocyte

Mature B or T cell that has not yet encountered its cognate antigen.

Activated Lymphocyte

Lymphocyte that has bound antigen and received the necessary signals to proliferate.

Effector Lymphocyte

Descendant of activated lymphocytes that actively performs immune functions (e.g., plasma cell).

Clonal Deletion (Negative Selection)

Elimination of self-reactive B cells during maturation to prevent autoimmunity.

Clonal Selection

Process by which an antigen selects and activates a B cell with a matching receptor.

Clonal Expansion

Rapid multiplication of activated lymphocyte clones after antigen recognition.

T-Dependent Antigen

Antigen (usually protein) that requires helper T-cell cytokines for B-cell activation and antibody production.

T-Independent Antigen

Antigen (often polysaccharide) that can directly activate B cells without T-cell help; induces mainly IgM and no memory.

Primary Immune Response

Initial antibody response upon first exposure to an antigen; slower, dominated by IgM.

Secondary Immune Response

Rapid, stronger antibody response upon subsequent exposure; characterized by higher IgG titers and memory cell activation.

Class Switching

Process in which a B cell changes the antibody class it produces (e.g., from IgM to IgG) without altering antigen specificity.

Immunological Memory

Long-term ability of the immune system to respond more effectively to previously encountered antigens.