Theoretical Models of Immune Processes - Immunological Computation: Theory and Applications - page 39

Sig 1

Co-stimulation

APC

Alarm signal

Distressed
cell

Normal
cell

Figure 2.6 Illustration of the DT model, which includes alarm signals as a part
of immune response.

She considers that there are, at least, four diff erent categories of stimulus, which
cause diff erent types of autoimmune diseases.

. An unrecognized infection in the target tissue. h is is not actually an autoim-
mune disease, because self-antigens are not the primary target. In this case,
although the immune system attempts to eliminate a pathogen, it ends up
damaging the target tissue.
2 . Molecular mimicry by a pathogen that has some similarity to a self-tissue. Some
pathogen-specifi c T cells also detect self-antigens and then, they respond
against both the pathogen and the self-tissues.
3 . Bad death. h is category is only considered in the DT model, as there are
no infectious agents and foreign components. Cells die permanently in our
bodies, and such deaths are controlled by some genes, which are subject to
mutations as all genes do. However, such mutations could induce alarm sig-
nals to initiate immune responses. Also, environmental toxins that cause cell
damage could lead to the release of such alarm signals.
4 . h e wrong class. As antibodies and cytokines released during an immune
response are potent molecules that are intended to eliminate pathogens, they
can damage some tissues, which are more sensitive to certain eff ector mol-
ecules than others. In this case, the immune system can kill a tissue with the
wrong class of immunity, although the response is not intended to attack that
particular tissue.

Figure 2.7 shows an abstract view of the antigen universe and illustrates the parti-
tions considered in classical SNS discrimination model and DT. According to the