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Immune functions traded for reproductive success

Immune functions traded for reproductive success

A sample of a deep-sea species of the devil species Melanocetus johnsonii, approximately 75 mm in size and fused on the abdomen with a 23.5 mm male. Credit: Edith A. Widder

Deep-sea anglerfishes use an incredible reproductive strategy. Tiny dwarfs permanently attach to relatively gigantic women, connect their tissues and then form a common bloodstream. In this way, the male becomes completely dependent on the female for the supply of nutrients, such as the developing fetus in the mother̵

7;s womb or the donor organ of the patient after transplantation. In the case of devils, this unusual phenomenon is called sexual parasitism and contributes to the reproductive success of these animals living in a vast area of ​​the deep sea, where women and men rarely meet.

Permanent attachment of males to females is a form of anatomical connection that is otherwise unknown in nature, with the exception of the rare occurrence in genetically identical twins. The immune system is an extraordinary barrier. It attacks foreign tissue because it would destroy cells infected with pathogens. They only witness the problems of organ transplantation in humans, which requires a long-term comparison of donor and recipient tissue types with immunosuppressants to ensure long-term organ transplant survival. But how is it possible that anglerfishes are so easily accepted when tissue rejection can be expected?

The phenomenon of sexual parasitism is a mystery that has existed for 100 years since the first tethered couple was discovered by an Icelandic fisheries biologist in 1920. Scientists from Germany and the United States have now solved this centenary and report their findings in a scientific journal. science.

Key functions of the immune system are eliminated

A few years ago, Thomas Boehm, a physician and immunologist at the Max Planck Institute of Immunobiology and Epigenetics in Freiburg, Germany, and Theodore W. Pietsch, an ichthyologist and internationally renowned anglerfish expert at the University of Washington in Seattle, decided to study the genomes of various species of marine fish. They began by looking at the structure of major histocompatibility antigens (MHC). These molecules are located on the surface of the body’s cells and signal an alarm to the immune system when the cells are infected with a virus or bacterium. To ensure that all pathogens are efficiently recognized, MHC molecules are extremely variable, so much so that it is difficult to find the same or nearly identical forms in any two individuals of a species. This property is the cause of the tissue mating problem that plagues human organ and bone marrow transplants.

Interestingly, the researchers found that anglerfishes that use a permanent attachment are largely depauperized in the genes encoding these MHC molecules, as evidenced by immune recognition in favor of tissue fusion. “In addition to this unusual constellation of MHC genes, we found that the function of killer T cells, which normally actively secrete infected cells or invade foreign tissues during the organ rejection process, was also severely numb, if not completely lost.” These findings suggest the possibility that the immune system of anglerfishes was very unusual among tens of thousands of vertebrates, ”said Jeremy Swann of the MPI in Immunobiology and Epigenetics and the first author of the study.

Immune functions traded for reproductive success

A female of the species Photocorynus spiniceps, 46 mm, with a 6.2 mm parasitic male fused to her back. Credit: Theodore W. Pietsch

Survival without acquiring immune devices

Following these unexpected discoveries, the researchers hypothesized that the reorganization of the anglerfishes immune system may be even more extensive than expected. Indeed, further research has shown that antibodies, which are the second strong weapon in the immune defense arsenal, are also lacking in some species of marine fish. “For humans, the combined loss of important immune devices observed in anglerfishes would result in fatal immunodeficiency,” said Thomas Boehm, MPI’s director of immunobiology and epigenetics and lead project scientist.

However, anglerfishes are, of course, able to survive without the necessary adaptive immune functions. The researchers concluded that animals use much better innate devices to defend themselves against infections, an unexpected solution to the problem facing all living things. Until now, it has been assumed that the partnership of acquired and innate immunity, once established in evolution, cannot be separated without serious consequences.

The immune system affects the reproductive strategy

The study thus shows that despite several hundred million years of joint evolutionary partnership of innate and adaptive functions, vertebrates can survive without adaptive immune devices that were previously considered irreplaceable. We assume that as yet unknown evolutionary forces first drive changes in the immune system, which are then used to develop sexual parasitism, “says Thomas Boehm.

Interestingly, scientists believe that they even caught one species from their fish collection on its way to the development of sexual parasitism. “We find it remarkable that an unusual method of reproduction has been invented several times independently in this group of fish,” says Ted Pietsch of the University of Washington.

Although details of improved innate immune devices in anglerfishes remain uncovered, the results of this study point to potential strategies that improve innate immune devices in human patients suffering from congenital or acquired immune damage. Therefore, the scientific journey, which began with vague observations on board a fishing vessel in the Mid-Atlantic, unexpectedly opens up new possibilities for treating immune disorders in humans.

The discovery of the immune system could end chronic organ rejection

More information:
JB Swann et al., “Immunogenetics of Sexual Parasitism” science (2020). science.sciencemag.org/lookup/… 1126 / science.aaz9445

Provided by the Max Planck Institute of Immunobiology and Epigenetics

Citations: Immune Functions Traded for Reproductive Success (2020, July 30) were acquired on July 30, 2020 from https://medicalxpress.com/news/2020-07-immune-functions-reproductive-success.html

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