Cytokines

Cytokines are produced by a lot of different types of cells, but primarily by CD4⁺ T-cells (Th, or helper T-cells) and macrophages.

The largest group of cytokines stimulates immune cell proliferation and differentiation.

Interleukin 1 (IL-1) activates T-cells
IL-2 stimulates proliferation of antigen-activated T and B-cells
IL-4, IL-5, and IL-6 stimulate proliferation and differentiation of B-cells
Interferon gamma (IFNg) stimulates macrophages, cytotoxic T cells (Tc-cells)
IL-3, IL-7 and GM-CSF stimulate hematopoiesis

Cytokines
Cytokine	Produced by	Target	Function
GM-CSF	Th-cells	Progenitor cells	Growth and differentiation of monocytes and dendritic cells
IL-1a IL-1b	Monocytes, Macrophages, B-cells, Dendritic cells	Th-cells	Co-stimulation, stimulates IL-2 production
		B-cells	maturation and proliferation
		NK cells	Activation
		Various	Inflammation, acute phase response*, fever
IL-2	Th₁-cells	Activated T and B cells, NK cells	Growth, proliferation, activation
IL-3	Th-cells, NK cells	Stem cells	Growth and differentiation
IL-3	Th-cells, NK cells	Mast cells	Growth and histamine release
IL-4	Th₂-cells	Activated B-cells	Proliferation and differentiation IgG and IgE synthesis
		Macrophages	Stimulates HLA Class II expression
		T-cells	Proliferation
IL-5	Th₂-cells	Activated B-cells	Proliferation and differentiation IgA synthesis
IL-6	Monocytes, Macrophages, Th₂-cells	Activated B-cells	Differentiation into plasma cells
		Plasma cells	Antibody secretion
		Stem cells	Differentiation
IL-7	Marrow stroma, Thymus stroma	Stem cells	Differentiation into progenitor B and T cells
IL-8	Macrophages, Endothelial cells	Neutrophils	Chemotaxis
IL-9	Th₂-cells	Th cells	Supports growth
IL-9	Th₂-cells	Stromal cells, fetal thymocytes	Enhances hematopoiesis in presence of EPO, IL-2, IL-3, IL-4
IL-10	Th₂-cells	Macrophages	Inhibits cytokine production
		NK cells	Inhibits cytokine production
		Th₁-cells	Inhibits cytokine production
IL-12	Macrophages, Dendritic cells	Activated Tc-cells	Growth factor, synergizes with with IL-2 to augment CTL response
		Th cells	Growth factor
		NK cells	Activation, growth factor, IFN-g production, enhances lytic activity
IFN-a	Leukocytes	Various	Inhibits viral replication Stimulates HLA Class I expression
IFN-b	Fibroblasts	Various	Inhibits viral replication Stimulates HLA Class I expression
IFN-g	Th₁-cells, Tc-cells, NK cells	Activated B-cells	Ig class switch to IgG (enhances complement fixation)
		Th₂-cells	Inhibits proliferation (stimulates Th1 proliferation)
		Macrophages	Stimulates HLA Class I & II expression, NO & ROI production, stimulates Fc receptor expression, stimulates secretion of TNFa, IL-1, IL-6, IL-8
		Tc-cells	Killing of virally infected cells and tumor cells
		NK cells	Killing of virally infected cells and tumor cells
TGF-b	T-cells, Monocytes	Monocytes, macrophages	Chemotaxis
		Activated macrophages	IL-1 synthesis
		Activated B-cells	IgA synthesis
		Various	Inhibits proliferation
TNFa	Macrophages, Mast cells, NK cells	Macrophages	CAM and cytokine expression
TNFa	Macrophages, Mast cells, NK cells	Tumor cells	Cell death
TNF-b	Th1 and Tc-cells	Phagocytes	Phagocytosis, NO production
TNF-b	Th1 and Tc-cells	Tumor cells	Cell death

* Acute phase proteins produced by the liver include:

C-reactive protein (CRP):

Opsonizes bacteria

Interacts with complement protein C1q to activate the classical complement pathway

Mannose binding lectin (MBL):

Opsonizes cells

Activates C2/C4 C3 convertase

Surfactant proteins A & D (SP-A & SP-D):

Bind cellular debris and dying cells with their globular heads, their tails are recognized by calreticulin associated with a-2 macroglobulin (CD91) on the surface of phagocytes