Cytokines and Thelper subsets

I. Characteristics of Cytokines (CKs)  CKs are small proteins (<30 kDa)  CKs are similar to hormones and growth factors.  CKs control the immune system.  Cytokines include subsets called lymphokines, monokines, chemokines, etc.

Cytokine Network  CKs are part of complex system that regulates the immune system.  CKs are primarily produced by immune system but many other organs (liver, brain, endocrine glands) make CKs to influence immune response.

Cytokine Network

T helper and Macrophage Interaction highlighted Effector T cell Th cells control immune system through CKs.

Activation of Cells = Production of Cytokines  Production of CKs is usually part of immune cell activation.  Cytokines are produced in response to different stimuli (e.g antigen receptor, cytokine/chemokine receptor).

T cell IL-2 IL-2 gene B cell IL-2 Receptor IL-4 Cytokine Network on a Local Level IL-4 Receptor IL-4 gene

II. Measuring Cytokines  Protein amount by ELISA. Good for in vitro experiments.  Protein amount by bioactivity assay using CK dependent cell lines.  RNA message by PCR.

Antigen Capture ELISA for IL-2

III. Actions of Cytokines  Autocrine acts on same cell that produced it. IL-2 for T cell activation  Paracrine acts on nearby cells. T cell help for B cells  Endocrine acts on cell at a distance (through bloodstream). Inflammatory cytokines.

Actions of Cytokines IL-2 for T-cell activation T-cell help for B cells Inflammatory cytokines

IV. Properties of Cytokines Pleiotropy  Same cytokine has different effects on cells can be activating or inhibiting.  Example: IL-10 can be inhibitory to macrophages and Th1 cells yet activating for Th2 cells and B cells.

Synergy Experimental Example Proliferation of CTLLs (CTLLs are cytokine dependent cell line)  Both IL-2 or IL-4 activate CTLLs in vitro.  Maximal proliferation obtained when both IL-2 and IL-4 added.  Both cytokines need to be blocked in order to inhibit growth.

Properties of Cytokines Pleiotropy Redundancy Synergy Antagonism

V. Functions Of Cytokines

VI. CD4 + T helper Subsets Th1/Th2 Cytokine Bias  CD4+ T helper cells can be divided into subsets based on their cytokine production.  T h 1 cells produce IL-2, IFN- , TNF-  CKs which activate cell mediated immunity  T h 2 cells activate IL-4, IL-6, IL-10 CKs that activate humoral immunity These Th subsets were originally identified using mouse T cell clones.

Mouse Th Subset Cytokine Th1 Th2 Table 12-4 from Goldsby

Th0 ---> Th1 or Th2 Original mouse experiments on Th cells (Mosmann et al (DNAX) 1986 J Immunol) Antigen specific T cells placed in culture with antigen and APCs to make T cell lines.  Spleen cells (T h 0) add IL-12  T h 1 cells  IL-2, IFN- , TNF-   Spleen cells (T h 0) add IL-4  T h 2 cells  IL-4, IL-6,IL-10  (T h 0 --precursor cell that produces IL-2, IL-4, and IFN- .)

Th1/Th2 Naïve T h 0 IL-2, IL-4, IFN-  IL-4 IL-12 Effector T h 1 cell IL-2, IFN-  Effector T h 2 cell IL-4, IL-6, IL-10

Th Cytokine Bias in Disease: Leprosy Skin disease caused by Mycobacterium leprae Lepromatous: has Th2 response and uncontrolled disease (leprosy). Tuberculoid: has Th1 response and limits disease (healing).

Cytokines as Ligands APC Target T Cell TNF-  or Lymphotoxin Ligand LT  and  Receptors Soluble or membrane bound Receptor

VII. Cytokine Receptors  Expression of cytokine receptors controls the ability of a cytokine to act on a cell.  Cell activation increases cytokine receptor expression.

Cytokine Receptor Families 5 different families of receptors based on common structural motifs. --> see book for more details

The Yin and Yang of Th1 and Th2 Immune Responses