Immune Cells

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Basophils

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They are the least common of the blood granulocytes. They are generated in the bone marrow and circulate in the periphery as fully differentiated forms. They have been implicated in as major effector cells during parasitic infection (during which they produce elevated amounts of IL-4) and allergic inflammation. These cells express both TLR2 and TLR4, and secrete IL-4 and IL-13 in response to TLR2 ligands, but not LPS. They can also be activated by complement 5a to produce cytokines and mediators. Their responses seem to be restricted to Th2 type immunity (Min B et al.).

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Dendritic Cells

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They are the most effective APCs capable of inducing robust CD4+ and CD8+ T cell immunity in vivo. After encountering pathogens in the peripheral tissues, They undergo a maturation program that leads to their migration into secondary lymphoid tissues. This migration is accompanied by the increase in the expression of MHC and costimulatory molecules and the production of cytokines leading to their enhanced ability to prime naïve T cells (Sato and Iwasaki). They are specialized APC for T cells and they play a predominant role in the stimulation of naïve T cells during primary immune responses. They not only activate lymphocytes, but they also make T cells tolerant of self-antigens (Wang et al, 1999). Antigen presented by dendritic cells that have not matured cause T cell anergy or deletion and induce T reg to secrete immunosuppressive cytokines.

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PDCs

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express B220 and intermediate levels of CD11c

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Follicular dendritic cells

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Specialized cells that reside in the primary follicles and germinal centers of secondary follicles in the lymph nodes where they interact with B cells and produce BAFF. They are of mesenchymal origin, are non-phagocytic, and lack lysosomes. MHC class II negative. They express complement receptors which enable these cells to trap complexed antigen very efficiently and hold it in its native form on their surface for extended periods. Memory B cells can then be stimulated by recognition of the retained antigen and costimulated through the B cell CD21 recognizing complement fragments held on the surface of the cell.

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gd T cells

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They do not appear to require antigen to be presented within the context of MHC molecules and are thought to be able to recognize soluble antigen like B cells. The majority do not express MHC, CD4, or CD8.

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Interdigitating dendritic cells

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Of bone marrow origin. Have the capacity to process four times their own volume of extracellular fluid in 1 hour, thereby facilitating antigen capture and processing in their abundant intracellular MHC class II-rich compartments.

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Langerhans cells

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Express intermediate to high levels of CD205 and langerin

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Mast cells

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In inflammatory lesion, they often do not display signs of explosive degranulation (K-G 2003). These cell lines can produce a panel of different cytokines including IL-3, IL-4, IL-5, IL-6, and IL-13, as well as GM-CSF and TNF (Hultner 2000). The cells may play a role in lethal sepsis (Carvalho 2005).

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NK cells

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Large granular leukocytes with a characteristic morphology. Lectin-like and other receptors on the cell serve to bring it and the target into close opposition. This activates the cell and leads to a polarization of granules between nucleus and target within minutes and extracellular release of their contents into the space between the two cells followed by target cell death. Perforin, TNFa, lymphotoxin-b, IFNg, and granzymes are contained in the granules. These cells kill by activating apoptosis. Granzyme B passes through a perforin membrane pore into the cytoplasm where it can split procaspase-8 and activate the apoptotic process.

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NKT cells

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Cells possessing the NK1.1 marker and a T cell receptor. Recognize lipid antigens presented by CD1d and constitute a major component of the T cell compartment (20-30% of bone marrow T cells and 1% of spleen cells). They can rapidly secrete IL-4 and IFNg upon stimulation.

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Plasma cell

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A single cell secretes millions of molecules of antibody but they are all identical and will be related to the single specificity of antibody used as the antigen receptor on the B-lymphocyte from which the plasma cell was derived.