B Lymphocyte Activation

Vocabulary flashcards covering key concepts of B cell activation, BCR signaling, germinal and extrafollicular responses, and T cell help.

B lymphocyte (B cell)

A lymphocyte that participates in humoral immunity by producing antibodies after activation.

BCR (B cell receptor)

Membrane-bound immunoglobulin complex that recognizes antigen and initiates B cell activation.

IgM

First antibody isotype produced by B cells; also present as the BCR on naive B cells.

IgD

Co-expressed with IgM on naive B cells and participates in antigen recognition.

Germinal center

Region within a secondary lymphoid follicle where B cells proliferate, mutate, and class-switch during an immune response.

Afferent lymphatic vessel

Lymphatic vessel that brings lymph into a lymph node.

High endothelial venules (HEVs)

Specialized blood vessels through which naive lymphocytes enter lymph nodes.

CD4+ T helper cell

T cell subset that provides help to B cells via CD40L and cytokines, enabling antibody responses.

CD40-CD40L interaction

Co-stimulatory signal between B cells (CD40) and activated CD4+ T cells (CD40L) promoting activation and differentiation.

Isotype switching

Genetic switch that changes the antibody class (e.g., IgM to IgG) while preserving antigen specificity; requires T cell help.

CD21 (CR2)

B cell receptor for the complement fragment C3d that can augment activation.

ITAM

Immunoreceptor tyrosine-based activation motif; signaling sequence in BCR/co-receptor that must be phosphorylated to activate signaling.

Blk, Fyn, Lyn

Protein tyrosine kinases that phosphorylate ITAMs to propagate BCR signaling.

NF-κB and NFAT

Transcription factors activated downstream of BCR signaling, leading to cytokine gene expression.

BCR crosslinking

Crosslinking of multiple BCRs by multivalent antigen, triggering receptor signaling.

CD19

B cell co-receptor that participates in BCR signaling.

Surrogate light chain

Part of the pre-B cell receptor that pairs with the heavy chain to test functionality during early B cell development.

RAG1

Recombination-activating gene 1; enzyme essential for V(D)J recombination.

RAG2

Recombination-activating gene 2; works with RAG1 in V(D)J recombination.

V(D)J recombination

Genetic process assembling BCR gene segments to create diverse antigen receptors.

Common Lymphoid Progenitor

Precursor giving rise to B, T, and NK lineages in the bone marrow.

Pro-B cell

Early B cell stage where heavy chain gene rearrangement begins.

Immature B cell

B cell stage after heavy/light chain rearrangement with surface IgM; undergoes selection.

Mature naive B cell

B cell that expresses surface IgM and IgD and has not yet encountered antigen.

Antigen processing in B cells

BCR-bound antigen is internalized into endosomal vesicles for processing and presentation.

Memory B cells

Long-lived B cells formed after activation that respond rapidly on re-exposure to antigen.