Maternal microchimerism in peripheral blood in type 1 diabetes and pancreatic islet beta cell microchimerism

Abstract

Maternal cells have recently been found in the circulation and tissues of mothers' immune-competent children, including in adult life, and is referred to as maternal microchimerism (MMc). Whether MMc confers benefits during development or later in life or sometimes has adverse effects is unknown. Type 1 diabetes (T1D) is an autoimmune disease that primarily affects children and young adults. To identify and quantify MMc, we developed a panel of quantitative PCR assays targeting nontransmitted, nonshared maternal-specific HLA alleles. MMc was assayed in peripheral blood from 172 individuals, 94 with T1D, 54 unaffected siblings, and 24 unrelated healthy subjects. MMc levels, expressed as the genome equivalent per 100,000 proband cells, were significantly higher in T1D patients than unaffected siblings and healthy subjects. Medians and ranges, respectively, were 0.09 (0-530), 0 (0-153), and 0 (0-7.9). Differences between groups were evident irrespective of HLA genotypes. However, for patients with the T1D-associated DQB1*0302-DRB1*04 haplotype, MMc was found more often when the haplotype was paternally (70%) rather than maternally transmitted (14%). In other studies, we looked for female islet beta cells in four male pancreases from autopsies, one from a T1D patient, employing FISH for X and Y chromosomes with concomitant CD45 and beta cell insulin staining. Female islet beta cells (presumed maternal) formed 0.39-0.96% of the total, whereas female hematopoietic cells were very rare. Thus, T1D patients have higher levels of MMc in their circulation than unaffected siblings and healthy individuals, and MMc contributes to islet beta cells in a mother's progeny.

Fig. 1.

MMc in T1D patients, unaffected siblings, and healthy subjects. A total of 172 probands were studied, 94 with T1D, 54 unaffected siblings, and 24 healthy controls. A panel of HLA-specific Q-PCR assays targeting nontransmitted, nonshared maternal HLA alleles was used (12) to test DNA extracted from whole peripheral blood. The amount of chimeric maternal DNA was expressed according to the number of genome equivalents present in 100,000 proband cells.

Fig. 2.

Female cells in male pancreas tissues. Immunohistochemistry for insulin and CD45 was used with concomitant FISH for X and Y chromosomes for the same cells as recently described (16). a, b, and c are from a boy with T1D and ketoacidosis; d, e, and f are from a boy with acute myeloblastic leukemia. (a) Fluorescence microscopy showing a female cell (arrowhead) with two (red) X chromosome signals. (Magnification: ×100.) Other cells contain one red and one Y chromosome (green) signal. Nuclei are identified with DAPI (blue). (b) Light microscopy of the same cells as in a. (Magnification: ×100.) The red-brown substrate identifies β cell insulin expression. (c) Overlay of a and b showing the identical cells with FISH and immunohistochemistry. (d) Fluorescence microscopy showing a female cell (arrowhead). (Magnification: ×100.) (e) Light microscopy of the same cells as in d. (Magnification: ×100.) (f) Overlay of d and e. Female cells were morphologically similar to surrounding β cells, and the cells did not express CD45.