THE CONTEXT
Antigen presentation can initiate an adaptive immune response or promote tolerance, while some antigens elicit antibodies without T-cell participation.
Professional and non-professional antigen-presenting cells
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Professional antigen-presenting cells are a specialised subset of hematopoietic lineage cells that efficiently prime unsensitised T cells and initiate a new adaptive immune response.
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Antigen presentation by non-professional antigen-presenting cells mostly produces T-cell tolerance or quiescent memory T cells.
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Lymphatic endothelial cells, neutrophils and mast cells are listed as non-professional antigen-presenting cells.
T-cell-dependent and T-cell-independent antigens
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T-cell activation is essential for responses to most antigens, including T-cell-dependent antigens such as proteins and erythrocytes.
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Polysaccharides and other structurally simple molecules with repeating epitopes are T-cell-independent antigens; antibody production against them does not require T-cell participation.
Requirements for T-cell recognition
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A T cell recognises processed antigen when an antigen-presenting cell displays it with MHC molecules and the T cell carries the receptor for that epitope.