Lymphoid Organs, T-cell and B-cell Development

These flashcards provide vocabulary definitions for the primary and secondary lymphoid organs, the stages of T-cell and B-cell development, and key concepts of the adaptive immune response based on the lecture transcript.

Lymphoid Organs

Organs involved in the production of immune cells and the sites for maturation, differentiation, and proliferation.

Maturation

The growth of a cell from the time that it is produced until such time that it is functional.

Differentiation

The specialization of cells regarding whether they will become cells of innate or adaptive immunity, or the activation of adaptive immunity cells into specific subsets like T helper or B cells.

Proliferation

The multiplication of cells into multiple cells of the same type.

Primary Lymphoid Organs

Sites of maturation for immune cells, which include the Thymus and Bone Marrow.

Secondary Lymphoid Organs

Sites of differentiation and proliferation where the first encounter with an antigen takes place for the adaptive immunity; examples include the Spleen, Lymph Nodes, and MALT.

Thymus

A primary lymphoid organ located along the sternum where T cells mature; it consists of a cortex for newly migrated cells and a medulla for newly formed cells.

Bone Marrow

The site where blood cells are produced and where B cells mature.

Red Pulp

A compartment of the spleen that serves as the site for the sequestration of RBCs.

White Pulp

A compartment of the spleen that serves as the site for the sequestration of phagocytes.

Lymph Nodes

Small secondary lymphoid organs divided into the cortex (B cells site), paracortex (T cells and antigen presenting cells site), and medulla (macrophages site).

MALT

Mucosa Associated Lymphoid Tissue, which includes GALT (Gut Associated Lymphoid Tissue), Peyer’s Patches, and BALT (Bronchi Associated Lymphoid Tissue).

Cutaneous Immune System

Immune cells located just below the skin.

Helper T cells

$CD4+$ cells that coordinate the immune response by activating other cells like B cells and macrophages.

Cytotoxic T cells

$CD8+$ cells whose purpose is to kill other cells, such as tumor cells or cells housing a virus.

Cluster of Differentiation (CD)

Markers or antigens found on the surface of cells, such as $CD4$ or $CD8$, used to identify specific cell types.

Double negative thymocytes

Early-stage T cells in the thymus that do not yet express either $CD4$ or $CD8$ markers.

Somatic rearrangement

Also known as somatic recombination, it is the random rearrangement of genes to produce a unique and specific T cell receptor (TCR) even before encountering an antigen.

Double positive thymocytes

Stage of T cell development where the cell expresses both $CD4$ and $CD8$ markers.

Negative selection

A selection process where T cells that react against the body's own antigens are killed or undergo apoptosis to prevent autoimmune diseases.

Antigen Presenting Cell (APC)

Cells like phagocytes that engulf antigens and present their components on the surface to activate T cells.

Interleukin-2 ($IL-2$)

A cytokine produced by activated T cells that further activates other T cells and promotes proliferation.

Naïve cell

A T cell or B cell that has not yet been exposed to an antigen; also referred to as a virgin cell.

Pre-B cell

A stage in B cell development in the bone marrow characterized by the production of $\mu$ chains inside the cell.

Immature B cell

A stage of B cell development where the cell first expresses $IgM$ on its surface as a receptor.

Mature B cell

A B cell that expresses both $IgM$ and $IgD$ antibodies on its surface and is released into the peripheral blood.

Plasma cell

A fully differentiated, activated B cell that secretes antibodies specific to the antigen that triggered its activation.

Primary Immune Response

The first-time encounter with a pathogen, typically characterized by the production of $IgM$ as the first antibody to appear.

Isotype switching

The process where activated B cells switch from producing $IgM$ to other types of antibodies such as $IgG$, $IgA$, or $IgE$.

Affinity maturation

The process during B cell differentiation where the receptor is refined to become more fit to the specific antigen.

Clonal expansion

The proliferation of a specific type of lymphocyte with the same specificity following activation by an antigen.

$$IgG$$

An antibody that appears later in the immune response and serves as a marker for recovery from infection or secondary exposure.