Antigen-presenting cell interactions macrophages

Although closely related, monocytes/macrophages (MO) possess features that are distinct from DCs. Due to their limited expression of T-cell costimulatory molecules, MO are not able to prime T cells de novo, but rather stimulate effector/memory T cells by the secretion of cytokines, which support T-cell proliferation. As DCs, MO differentiate from myeloid precursors and form a heterogeneous population of antigen-presenting cells (APCs) that link the innate and adaptive immune systems. However, their ability to interact with T cells via MHC class II TCR interaction(s) as well as engagement of T-cell costimulatory receptors on their surface, makes close contact between MO and Tregs likely to occur in vivo. 

The class II proteins are produced mainly within specific cells, known as antigen-presenting cells (APC). Their role is to prepare antigens derived from the pathogens in such a way that they can interact with the T-helper cell receptor. Since this is their only role, they are sometimes called professional antigen-presenting cells , i.e. other immune cells can also present peptides to T-helper cells (e.g. macrophages, B-lymphocytes) but this is not their prime role. The professional APCs are also known as dendritic cells. 

Helper T Lymphocytes (CD4) recognize viral or bacterial antigens together with MHC class II molecules on surface of antigen presenting cell, such as a macrophage. Interaction leads to cytokine secretion, initiating a cascade of iimnune reactions. 

Cutaneous inflammatory T-ceU-mediated immune activation requires two T-ceU signals that are mediated via cell-cell interactions by surface proteins and by antigen-presenting cells (APC) such as dendritic cells or macrophages. 

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