Microchimerism - not all human cells in your body come from you | Thomas Kroneis | TEDxMedUniGraz

Key Concepts

• Chimerism: The presence of cells from one individual within another individual.
• Mount Chimera: A location in Turkey known for continuously burning fires due to natural gas evaporation, which inspired the myth of the Chimera creature.
• Chimera (Mythological Creature): A hybrid creature described as having the body of a lion, the head of a goat protruding from its back, and a snake as a tail.
• Microchimerism: A specific form of chimerism involving a very small number of cells from one individual present in another.
• Fetal Microchimerism: The presence of fetal cells in the mother's body, and maternal cells in the baby's body, which occurs during pregnancy and persists after birth.
• Germ Layers: The three primary layers of cells (ectoderm, mesoderm, and endoderm) that form during early embryonic development, from which all tissues and organs arise.
• Placenta: An organ that develops in the uterus during pregnancy, providing oxygen and nutrients to the growing baby and removing waste products from the baby's blood.
• Blood-Brain Barrier: A protective barrier that separates the circulating blood from the brain and central nervous system, preventing unwanted substances from entering the brain.

Chimerism: From Myth to Molecular Biology

This presentation explores the concept of chimerism, starting with its mythological origins and progressing to its scientific understanding in molecular biology, particularly focusing on microchimerism.

The Myth of the Chimera and its Real-World Inspiration

The speaker begins by referencing Mount Chimera in Turkey, a site characterized by natural gas evaporation causing continuous fires. This phenomenon, observed by ancient peoples, is suggested to be the inspiration for the mythological creature, the Chimera. The Chimera was believed to be a hybrid creature, often depicted with the body of a lion, the head of a goat, and a snake's tail, reflecting the co-existence of these animals in the region and the perceived "toxic breath" causing the fires.

Defining Chimerism

The core definition of chimerism is presented as "the presence of cells from one individual in another individual." An example provided is organ transplantation, where a recipient hosts cells from a donor.

Visualizing Chimerism: Animals and Humans

The presentation then delves into visual examples of chimerism:

• Animals: The speaker shows images of cats with distinct color patterns on different sides of their faces, such as "Venus" and "Chimera Naria," which appear as if two different cats have been combined. These are presented as examples of animals exhibiting chimerism.
• Humans: A compelling case study of a woman named Lydia is detailed. Lydia faced legal challenges to prove her maternity for financial support due to DNA test results that indicated she was not the biological mother of her children. Despite witnessing the births and having her mother and gynecologist as witnesses, she was accused of fraud. The breakthrough came when scientists discovered she was a chimera. It was determined that during early pregnancy, she had a twin sister who did not survive. Lydia absorbed her twin's cells, and these cells ended up in her reproductive organs. Consequently, the DNA of her children matched her deceased twin sister's cells, making Lydia genetically the aunt of her own children. This was confirmed by testing DNA from different parts of Lydia's body, with the vaginal swab yielding the matching DNA.

Microchimerism: A Ubiquitous Phenomenon

The concept of microchimerism is introduced as a more common and subtle form of chimerism.

• Definition: Microchimerism involves a very small number of cells from one individual present in another.
• Origin: This phenomenon begins during pregnancy, with cells from the mother transferring to the fetus and vice versa. These fetal cells can be found throughout the mother's organs even after birth, and similarly, maternal cells can be found in the offspring.
• Prevalence: The speaker asserts that "most likely all here in this room are micro chimera," meaning individuals likely host cells from their mothers, and mothers host cells from their children.
• Cell Types: Microchimeric cells can differentiate into various cell types, including blood cells and neurons, suggesting they possess stem cell-like properties.
• Multigenerational Aspect: Research has even found cells of grandmothers in the blood of babies, indicating a multigenerational aspect to microchimerism.
• Evolutionary Link: Microchimerism is linked to the evolution of internal gestation and the development of the placenta.
• Crossing Barriers: Importantly, these microchimeric cells can cross the blood-brain barrier, as evidenced by the detection of male (son's) cells in the brain of a female (mother). This is demonstrated through staining techniques that identify the Y chromosome.

Potential Roles and Implications of Microchimerism

While the exact functions of microchimerism are still being researched, several associations and potential benefits are discussed:

• Tissue Repair: Microchimeric cells have been shown to repair damaged tissue. An example with mice demonstrates fluorescent fetal cells migrating to an injured area in the mother's ear and integrating into the tissue, contributing to its renewal.
• Psychological Impact: A powerful anecdote highlights the potential psychological benefit of understanding microchimerism. A student who lost her mother to cancer found comfort in the knowledge that she was still hosting her mother's cells, offering a sense of continued connection.

Conclusion

The presentation concludes by emphasizing the profound and often overlooked phenomenon of chimerism, particularly microchimerism. It highlights how this biological reality, once confined to myth, is now understood at a molecular level, with potential implications for tissue repair and even psychological well-being. The speaker suggests that microchimerism is a fundamental aspect of human biology, connecting individuals across generations.