microchimerism

Microchimerism is the presence of a small population of cells within one individual that originated from a genetically distinct individual. These cells are not simply circulating DNA fragments; they are living cells that can persist and proliferate in the host.

Natural occurrences of microchimerism often arise during pregnancy. Fetal cells can cross the placenta and reside in the mother, while maternal cells can persist in the offspring. Twin pregnancies, miscarriages, or abortions can also contribute to cell exchange. In adulthood, microchimerism can arise after organ or bone marrow transplantation and, less commonly, through blood transfusions.

The cells involved in microchimerism can persist for years or even decades and may be found in various tissues, including blood, bone marrow, skin, liver, and other organs. Detection relies on genetic methods such as polymerase chain reaction for non-host alleles, fluorescence in situ hybridization for sex chromosomes, and increasingly sequencing-based approaches to identify donor-derived cells.

Clinical and biological relevance remains an active area of study. Demonstrated patterns include fetal microchimerism in women who have carried male fetuses (detectable via Y chromosome markers) and maternal microchimerism in offspring (detectable via maternal alleles). Associations have been reported between microchimerism and autoimmune diseases, such as scleroderma, or pregnancy-related complications, but causality is not established. In transplantation biology, donor-derived microchimerism has been linked to graft tolerance in some cases, while its role in others is less clear. Some researchers also speculate a role in tissue repair, though evidence is not definitive.

Ongoing research aims to clarify mechanisms, prevalence, and the true clinical significance of microchimerism.