Immunology

Perforin

A protein in the cytoplasmic granules of both cytotoxic T lymphocytes and natural killer cells that creates transmembrane pores for delivery of granules content into target cells. Structurally and chemically related to C9 protein of complement which performs a similar function.

Granulysin

An antimicrobial that induces apoptosis.

Lipopolysaccharide, LPS

An endotoxin found on the bacterial cell membrane of a gram-negative bacterium.

Signal 1 of naive T cell activation

Antigen presented on MHC II are recognized by T cell receptors on T helper cells, and antigen presented on MHC I are recognized by cytotoxic T cells.

Antigen presenting cells (APCs)

B cells, macrophages, and dendritic cells.

Signal 2 of naive T cell activation

"Co-stimulatory signal" is given by interaction of B7 and CD28.

IgE

*Binds mast cells and basophils *Mediate immediate, type I, hypersensitivity through release of inflammatory mediators such as histamine *Mediate immunity to worms by activating eosinophils

Major histocompatibility complex (MHC)

*Cell surface molecules encoded by HLA genes. *Present antigen fragments to T-cells and bind T-cell receptors.

Regulatory T cells

*Help maintain specific immune tolerance by suppressing CD4 and CD8 T-cell effector functions. *Activated regulatory T cells produce anti-inflammatory cytokines like interleukin (IL) 10 and transforming growth factor, TGF-beta.

Cytotoxic T cells (CTLs)

*Lymphocytes with CD8 that kill virus-infected, neoplastic, and donor graft cells by inducing apoptosis

IgG

*Main antibody in secondary (delayed) response to an antigen *Most abundant isotype in serum *Crosses placenta to provide infants with passive immunity

IgA

*Prevents attachment of bacteria and viruses to mucous membranes *Crosses epithelial cells by transcytosis *Released into secretions and early breast milk

Helper T1 cells

*Secrets IFN-gamma *Activates macrophages and cytotoxic T lymphocytes (CTLs) *Inhibited by interleukin 4 (IL4) and interleukin 10 (IL10) from helper T2 cells

Helper T2 cells

*Secrets interleukin (IL) 4, 5, 6, and 13 *Recruits eosinophils for parasite defense and promotes IgE production by B cells *Inhibited by interferon (IFN) gamma from helper T1 cells

Natural killer, NK, cells

*Use perforin and granzymes to induce apoptosis of virally infected and tumor cells. *Only lymphocyte member of the innate immune system. *Kills when exposed to a nonspecific activation signal or an absence of class 1 MHC on cell surface and via antibody-dependent cell-mediated cytotoxicity, ADCC.

Human leukocyte antigen

A group of protein molecules located on bone marrow cells that can provoke an immune response

Granzyme B

A serine protease that activates apoptosis inside target cells.

Fragment constant (Fc)

Constant portion of heavy chain that fixes complement

Negative selection

Elimination of autoreactive T-cells. Eliminate T cells that express T cell receptors with high affinity for self antigens and are autoreactive.

Acute-phase reactants

Factors of which serum concentrations change significantly in response to inflammation

Antibody-dependent cell-mediated cytotoxicity, ADCC

Lysis of target cells coated with antibody by effector cells with cytolytic activity and specific immunoglobulin receptors called Fc receptors. Effector cells include natural killer cells, macrophages, and granulocytes.

Toll-like receptors, TLRs

Pattern recognition receptors that recognize pathogen-associated molecular patterns, PAMPs, such as LPS, flagellin, and ssRNA.

IgM

Produced in primary (immediate) response to an antigen

Positive selection

Select for T cells that express T cell receptors capable of binding surface self MHC molecules. Double-positive thymocytes (CD4+/CD8+) survive and move deep into the thymic cortex.

Thymus

Site of T-cell differentiation and maturation.

Fragment antigen binding (Fab)

Variable part of light and heavy chains that recognizes antigens