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

 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

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. P leiotropic -different cell types to secrete the same cytokine or for a single cytokine to act on several different cell types

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

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

 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).

FeatureMHC Class IMHC 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 residue10-30 residue NomenclatureHLA-A, HLA-B, HLA-C HLA-DP, HLA- DQ HLA-DR