DISCRIMINATION BETWEEN SELF AND NON-SELF:

The discrimination between self and non-self is fundamental to immunology. Clones of cells which have the capacity to recognize self antigens are eliminated early (usually neonatally) in an animal’s development. This “clonal deletion”, which occurs possibly by processes involving programmed cell death (apoptosis), is not yet fully understood, but is known to produce tolerance to self antigens. Tumour cells can be destroyed by immune processes if they express antigens that are not present on normal cells (the so-called “tumour associated antigens”). The magnitude of the immune response against an antigen is often considerably affected by the difference between its structure and that of host antigens, and by the extent of recruitment of “help” (largely mediated by T-cells) for the antigen.