CYTOKINESCytokines are a diverse group of non-antibody proteins released by cells that act as intercellular mediators, especially in immune processes

Definition

Cytokines are a diverse group of non-antibody proteins released by cells that act as intercellular mediators, especially in immune processes

Cytokines…..

Low molecular weight soluble proteins (polypeptides) produced in response to microbes and other antigens

They act via cell surface receptors to mediate and regulate the amplitude and duration of the immune-inflammatory responses, through activation of macrophages, controlling growth and differentiation of T and B cells

General Properties

1.Produced by cells involved in both natural and specific immunity

2. Mediate and regulate immune and inflammatory responses

3. Secretion is brief and limited not stored as pre-formed molecules

4. Synthesis is initiated by new short-lived gene transcription

mRNA is short-lived 5. Pleiotropic -different cell types to

secrete the same cytokine or for a single cytokine to act on several different cell types

•6. Redundancy -similar functions can be stimulated by different cytokines. Receptors for cytokines that can be grouped into families in which one subunit is common to all members.

7. Often influence the synthesis of other cytokines

They can produce cascades, or enhance or suppress production of other cytokines

They exert positive or negative regulatory mechanisms for immune inflammatory responses

8. Often influence the action of other cytokines. antagonistic -cytokines causing opposing activities

additive - two or more cytokines acting together synergistic -two or more cytokines acting

together (greater than additive)

8. Bind to specific receptors on target cells with high affinity..

9. Cellular responses to cytokines are generally slow (hours), require new mRNA and protein synthesis

Major Histocompatibility Complex

MHC

The Cellular mediated immune system relies on many regulatory mechanisms and it main controller is Major Histocompatibility Complex (Mhc).

MHC

MHC molecules are cell surface receptors that bind antigen fragments and display them to various cells of the immune system, most importantly T-cells.

Major Histocompatibility Complex

The binding of peptides by an MHC-I or MHC-II molecule is the selective event

Permits the cell expressing the MHC molecule (APC) to sample

1. its own proteins (in the case of MHC-I)

2. the antigen proteins ingested (in the case of MHC-II).

MHC I vs MHC IIFeature MHC Class I MHC class II

Polypeptide Chain

α (44-47 kD)2 (12 kD)

α (32-34 kD) (29-32 kD)

Location of antigen peptide bind

α1 and α2 domains α1 and 1 domains

Size of antigen peptide

8-11 residue 10-30 residue

Nomenclature HLA-A, HLA-B, HLA-C

HLA-DP, HLA-DQ HLA-DR