Page 1198 - Veterinary Immunology, 10th Edition

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FIG. 36.3 Viruses may trigger autoimmune responses either by
molecular mimicry or by bystander activation.

Microchimerism

During pregnancy, mothers and their fetuses may exchange a few

cells. Some of these fetal cells may persist in a mother's body for
many years after pregnancy. Conversely, a mother's cells may
survive for many years in her offspring. These cells are accepted by

a tolerant immune system. The process is called fetal
microchimerism, and it has been suggested that these persistent
cells may be the cause of some autoimmune diseases. In women
with the autoimmune disease scleroderma, it is possible to find fetal
T, B, and natural killer (NK) cells, as well as fetal monocytes, in

their blood. It has been suggested, therefore, that scleroderma is a
form of graft-versus-host disease in these patients. Transfer of cells
from mother to her fetus may also cause autoimmunity. For
example, small numbers of maternal cells can be detected in the

blood of most boys with the autoimmune disease dermatomyositis.
In all these cases, the number of persistent foreign cells is so small
that they cannot be the sole cause of the autoimmune disease.

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