Can maternal microchimeric cells influence the fetal response toward self antigens?

Feto-maternal allo-immunity, regulatory T cells and predisposition to auto-immunity. Does it all start in utero?

During gestation, maternal cells traffic to the fetus leading to the natural phenomenon of microchimerism. Although their persistence in offspring has been associated with several autoimmune disorders, the precise role of maternal cells in these disorders remains unclear. We aimed to evaluate whether alloreactive maternal T cells could directly trigger a graft-vs.-host like reaction or indirectly influence the development of the offspring's regulatory T cells (Treg) favoring autoimmunity. In a specific breeding strategy, we recently reported that maternal allogeneic T cells changed fetal Treg development and their quantities in mesenteric lymph nodes, leading to early signs of inflammation in the gut later in life. Although maternal microchimeric T cells were found in newborn tissues, we could not detect any cells in the gut from adult offspring where the inflammation occurred. Thus, strongly alloreactive maternal microchimeric T cells may indirectly drive the offspring to gut inflammation. We believe these results suggest a new mechanism for predisposition to auto-immunity.

Maternal microchimerism: friend or foe in type 1 diabetes?

Increased levels of non-inherited maternal HLA alleles have been detected in the periphery of children with type 1 diabetes and an increased frequency of maternal cells have been identified in type 1 diabetes pancreas. It is now clear that the phenotype of these cells is pancreatic, supporting the hypothesis that maternal cells in human pancreas are derived from multipotent maternal progenitors. Here we hypothesize how increased levels of maternal cells could play a role in islet autoimmunity.

Selective organ specific inflammation in offspring harbouring microchimerism from strongly alloreactive mothers

The origins of autoimmunity are not yet understood despite significant advances in immunology. The trafficking of maternal cells to the offspring represents the very first immunological event in foetal life and is reinforced during lactation. The persistence of maternal cells in offspring's tissues and circulation has been associated with several autoimmune disorders. However a direct causal effect has never been demonstrated. Maternal T cells specifically targeting foetal insulin producing cells have been shown to generate islet inflammation without directly participating in this process. Our objective was to evaluate if alloreactive maternal cells could directly trigger a graft-versus host like reaction or indirectly influence the development of the offspring's regulatory T cells favouring autoimmunity. We adopted a breeding strategy comparing genetically identical offspring from either strongly alloreactive transgenic mothers compared to immunodeficient mothers. We detected maternal alloreactive T cells in the offspring and early signs of inflammation in small intestine of 6 weeks old offspring. Interestingly, CD4(+) Foxp3(+) regulatory T cell frequency was diminished in mesenteric lymph nodes from eight months old offspring born of alloreactive mothers compared to offspring of immunodeficient mothers. Our study favours a hypothesis where highly alloreactive maternal cell microchimerism indirectly predisposes offspring to autoimmunity.

Pregnancy-acquired fetal progenitor cells

The transfer and persistence of fetal progenitor cells into the mother throughout pregnancy has sparked considerable interest as a trafficking stem cell and immunological phenomenon. Indeed, the intriguing longevity of semi-allogeneic fetal microchimeric cells (FMC) in parous women raises questions over their potential clinical implications. FMC have been associated with both immune-modulatory roles and participation in maternal tissue repair. Although their influence on maternal health is as yet unresolved, FMC selectively home to damaged maternal tissues and often integrate, adopting site-appropriate phenotypes. FMC features, such as plasticity and persistence in their maternal host, suggest that they likely include pluripotent, or various multipotent and committed stem and progenitor cells. Recent efforts to determine what cell types are involved have established that FMC include cells of ectodermal, endodermal, mesodermal, and perhaps trophectodermal lineages. This review details FMC phenotypes and discusses how FMC themselves may be considered a naturally occurring stem cell therapy.

The otherness of self: microchimerism in health and disease

Microchimerism (Mc) refers to the harboring of a small number of cells (or DNA) that originated in a different individual. Naturally acquired Mc derives primarily from maternal cells in her progeny, or cells of fetal origin in women. Both maternal and fetal Mc are detected in hematopoietic cells including T and B cells, monocyte/macrophages, natural killer (NK) cells and granulocytes. Mc appears also to generate cells such as myocytes, hepatocytes, islet β cells and neurons. Here, the detrimental and beneficial potential of Mc is examined. The prevalence, diversity and durability of naturally acquired Mc, including in healthy individuals, indicates that a shift is needed from the conventional paradigm of 'self versus other' to a view of the normal 'self' as constitutively chimeric.