Acquired Immunity - Part 2: Lymphocyte Ontogeny, Activation, and Tolerance

Flashcards covering the ontogeny of B and T lymphocytes, lymphoid organs, T-helper cell subsets, and mechanisms of self-tolerance based on the lecture Acquired Immunity - 2.

Primary lymphoid organs

The sites where precursors of T and B lymphocytes are produced and mature. Includes bone marrow and the thymus.

Secondary lymphoid organs

Where mature lymphocytes reside and mediate their responses to antigens; includes the spleen, lymph nodes, and Mucosa-associated lymphoid tissue (MALT).

Spleen

A secondary lymphoid organ responsible for the immune response to antigens originating from the blood.

Lymph nodes

Secondary lymphoid organs that facilitate the immune response to antigens originating from tissues.

Mucosa-associated lymphoid tissue (MALT)

Lymphoid tissue that mediates the immune response to antigens encountered at mucosal surfaces.

Ontogeny of B-lymphocytes

Pre-B-lymphocytes = bone marrow. Once in the blood = mature B lymphocytes (have biomarkers: IgD, monomeric IgM, MHCII). Mature B-lymphocytes reside in secondary lymphoid tissues.

Ontogeny of T-lymphocytes

Pre-T-lymphocytes = bone marrow. Then they “go to school” in the thymus; immature T-lymphocytes (biomarkers: CD4,CD8, TcR). Any autoreactive immature T-lymphocytes are destroyed. Remaining cells are “educated” to recognize MHCI (CD8+; T-cytotoxic) or MHCII (CD4+; T-helper).

$$CD19-21$$

Unique surface markers found on $B$ cells used for identification.

$$CD40$$

A surface marker on $B$ cells that receives activation signals from $T$ cells.

Th1 subset

A type of $CD4^+$ $T$-helper cell induced by $IFN\text{-}\text{γ}$ and $IL\text{-}12$ that secretes $IL\text{-}2$ and $IFN\text{-}\text{γ}$ to activate macrophages and stimulate $T$-cytotoxic cells. Protect against intracellular pathogens; “cell-mediated immunity”

Th2 subset

A type of $CD4^+$ $T$-helper cell that secretes $IL\text{-}4$, $IL\text{-}5$, $IL\text{-}9$, and $IL\text{-}13$ to activate $B$-lymphocytes against extracellular pathogens.

$Th17$ subset

A type of $CD4^+$ $T$-helper cell that produces cytokines such as $IL\text{-}17$, $IL\text{-}22$, and $IL\text{-}21$.

$Tf$ (Follicular T-helper cells)

A subset of $CD4^+$ cells that secrete $IL\text{-}4$ and $IL\text{-}21$ to facilitate interaction with and activation of $B$ cells.

$Treg$ (T-regulatory cells)

A subset of $CD4^+$ cells that secrete $IL\text{-}10$ and $TGF\text{-}\text{β}$ to suppress autoreactive cells and maintain self-tolerance.

$IFN\text{-}\text{γ}$ (Interferon-gamma)

A cytokine also known as macrophage-activating factor that enhances the intracellular killing capacity of macrophages.

Cell-mediated immunity

An immune response involving $Th1$ cells, $T$-cytotoxic cells, and $NK$ cells, primarily effective against intracellular pathogens and tumor cells.

Humoral-mediated immunity

An immune response centered on $B$-lymphocyte activation and differentiate into plasma cells that produce antibodies against extracellular pathogens.

Anergy

A mechanism of self-tolerance where autoreactive lymphocytes are made non-responsive to their target antigens.

Ignorance (Self-tolerance)

A state where autoreactive lymphocytes do not react because the self-antigen is sequestered (hidden) or present in very low concentrations.

Primary response

The initial, usually slow immune response to an antigen where $IgM$ is the predominant antibody produced.

Secondary response

A faster and stronger immune response upon subsequent exposure to an antigen, characterized by the production of $IgG$, $IgA$, or $IgE$.