Immune responses, types

Immune responses can be divided into type 1 and type 2, based on the pattern of cytokine secretion and functional outcome of the immune response. Type 1 immune responses are characterized by secretion of IFN-gamma, production of IgG2a in mice, and activation of macrophages, NK cells, and cytotoxic T-cells. Type 2 responses are characterized by secretion of IL-4, IL-5, and IL-13 and by IgGl and IgE production. The responses are reciprocally regulated. How the polarization of the immune response toward type 1 or type 2 is determined is not exactly understood. IL-12 is an important factor that drives the type 1 response, and IL-4 is implicated in the type 2 response. Microbial products such as LPS and bacterial DNA stimulate the secretion of IL-12 by dendritic cells and preferentially induce type 1 immune responses. 

There are two general types of immune responses to foreign antigens the cell-mediated immune response (type 1 or Thl) and the antibody-mediated... 

Contamination of blood products with lymphocytes can lead to transfusion-induced reactions ranging from a mild fever to severe reactions such as alloimmunization and graft versus host disease (GvHD), in which the transfused lymphocytes (graft) survive the defensive immune reaction of the patient (host) and start a reaction which destroys the cells of the host. The patient also may develop an immune response to the human leukocyte antigen (HLA) type of the graft s cells and reject all platelet transfusions that do not match their own HLA system. The HLA system, found on blood platelets and lymphocytes, is more compHcated than, but similar to, the ABO blood group system of red cells. 

Chemical-mediated immune suppression has been identified from the experimental study of several wildlife species. Harbour seals fed either chemically contaminated fish from the Wadden Sea or imcontaminated fish were found to have differing immune responses, with the exposed group showing lowered immune response to microbial infections and certain types of cancer. "" Mink fed fish taken from below a discharge point for bleached Kraft pulp mill effluent have also shown impaired immune function, " showing that the non-accnmillative chemicals in this effluent can actively disrupt endocrine associated functions. 

There are a number of practical problems involved with using polysaccharides as vaccines as there are frequently too many different chemotypes for it to be practicable to prepare a vaccine. In some cases a limited number of serotypes are the dominant cause of infection and it may then be possible to produce vaccines. A major problem is the poor immune response elicited by polysaccharide antigens, which may in some cases be improved by chemical modification. This is (fie case for vaccines for Haemophilus influenzae type b (a causative agent of meningitis), where the antigenicity of the polysaccharide can be increased by coupling to proteins. 

The key end result of TLR signalling is the induction of cytokines. Cytokines are proteins produced during an immune response that allow the maturation, activation and differentiation of effector cells in the immune system. The activation of NFkB and AP-1 by the MyD88 and the TREF dependent pathways leads to the production of proinflammatory cytokines such as IL-6, TNF-a and various chemokines. This pathway can also activate IRF-7 via TLR-7and TLR-9 allowing Type-I interferons to be produced. 

Type I allergic reactions are inappropriate immune responses to an allergen with preferential synthesis of immunoglobulin E (IgE), a special antibody class, which binds to mast cells and basophilic granulocytes via Fee receptors. Binding of the allergen to the cell-bound IgE initiates the rapid release of allergic mediators, most prominently histamine, and the de novo synthesis of arachidonic acid metabolites and cytokines, which are responsible for the clinical symptoms. 

Cell-mediated immunity (CMI) is the result of the activity of many leukocyte actions, reactions, and interactions that range from simple to complex. This type of immunity is dependent on the actions of the T lymphocytes, which are responsible for a delayed type of immune response The T lymphocyte becomes sensitized... 

There is only one known type II IFN, IFN-y, discovered in 1965 (Wheelock and Sibley 1965). IFN-y is exclusively produced by immune cells, such as activated thymus-derived T cells and natural killer (NK) cells, after stimulation by foreign antigens or mitogens in the early stages of the innate immune response (Boehm etal. 1997). The human IFN-y gene maps to chromosome 12. IFN-y is a noncovalent... 

Honda K, Yanai H, Negishi H, Asagiri M, Sato M, Mizutani T, Shimada N, Ohba Y, Takaoka A, Yoshida N, Taniguchi T (2005) IRF-7 is the master reguiator of type-I interferon-dependent immune responses. Nature 434 772-777... 

Inhibition of human allergic T-helper type 2 immune responses by induced regulatory T cells requires the combination of interleukin- 10-treated dendritic cells and transforming growth factor-p for their induction. Clin Exp Allergy 2006 36 1546-1555. 

Innate immune response to viral infections is predominately through interferon-alpha, -beta (IFN-a and -P) induction and activation of natural killer (NK) cells. Although viral replication can induce IFN-a and -P expression, macrophages are capable of producing and secreting cytokines which also induce the production of these type I interferons (Falk 2001). Bound IFNa and p to its receptors on NK cells increases its ability to lyse virally-infected cells. 

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