Deep-sea anglerfishes use an extraordinary reproductive strategy. The little dwarf males are permanently associated with relatively giant females, fuse their tissues together, and then establish a normal blood circulation. In this way, the male is completely dependent on the female for the supply of nutrients, like a developing fetus in her mother̵7;s womb or a donor organ to a transplant patient. In anglerfish, this unusual phenomenon is termed as sexual parasitism and contributes to the reproductive success of these deep-sea animals, where females and males meet differently.
Permanent attachment of males to females represents a form of anatomical union, which is otherwise unknown in nature, except in rare cases in genetically identical twins. The immune system presents an extraordinary barrier. Attacks foreign tissues as it would destroy pathogen-infected cells. Just testify to the difficulties associated with organ transplantation in humans, which requires careful matching of donor and recipient tissue types, along with immunosuppressive drugs, to ensure the long-term survival of the organ graft. But how is it possible for anglerfish to accept each other so easily when tissue rejection is expected?
The phenomenon of sexual parasitism has posed an enigma that has existed for 100 years, since the first attached couple was discovered by an Icelandic Icelandic biologist in 1920. Now, scientists from Germany and the US have solved this age-old story and report the findings to scientific journal science.
The main functions of the immune system eliminated
A few years ago, Thomas Boehm, a physician and immunologist working at the Max Planck Institute for Immunobiology and Epigenetics in Freiburg, Germany, and Theodore W. Pietsch, an ichthyologist and internationally renowned expert on anglerfish working at the University of Washington in Seattle, set to study the genomes of various anglerfish species. They began by looking at the structure of major histocompatibility (MHC) antigens. These molecules are found on the surface of cells in the body and signal to the immune system when cells are infected with a virus or a bacterium. To ensure that all pathogens are identified efficiently, MHC molecules are so variable that it is difficult to find identical or nearly identical forms in each of the two individuals of a species. This feature is at the root of the tissue-matching problem that prevents the transplantation of the human organ and bone marrow.
Interestingly, the researchers found that anglerfats that use permanent adhesions are mostly haunted by genes encoding these MHC molecules, as if they had removed the recognition of immunity 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 eliminate infected cells or attack foreign tissue during the organ rejection process, was also unclear if they are not lost. “These findings suggest that the possibility that the anglerfishe’s immune system was very unusual among tens of thousands of vertebrate species,” says Jeremy Swann of the MPI of Immunobiology and Epigenetics and lead author of the study.
Survival without acquired immune facilities
Following these unexpected discoveries, scientists suspected that the reorganization of the anglerfish immune system may be even more extensive than expected. And indeed, further research has shown that antibodies, which are the second most powerful weapon in the arsenal of immune defenses, are also lacking in some species of anglerfish. “For humans, the combined loss of important immune objects observed in anglerfishes will result in fatal immunoduction,” says Thomas Boehm, Director at the MPI of Immunobiology and Epigenetics and the project’s lead scientist.
However, anglerfish is clearly capable of surviving without essential adaptive immune functions. Thus, the researchers concluded that animals use highly improved innate facilities to protect themselves from infections, a sudden solution to a problem faced by all living things. Indeed, until now, it was thought that a partnership of acquired and innate immunity, once formed in evolution, could not disintegrate without serious consequences.
The immune system affects the reproductive strategy
The study thus shows that despite several hundred million years of co-evolutionary partnership of innate and adaptive functions, vertebrates can survive without adaptive immune devices that were previously considered irreplaceable. “We assume that evolutionary forces, but unknown, initially trigger changes in the immune system, which are then used for the evolution of sexual parasitism,” says Thomas Boehm.
Interestingly, scientists believe that, among their collection of fish, they have even caught a species on the way to the development of sexual parasitism. “We find it remarkable that the unusual mode of reproduction was invented several times independently in this group of fish,” says Ted Pietsch of the University of Washington.
Although details of improved anglerfish-born immune facilities remain to be discovered, the results of this study point to possible strategies that strengthen innate immune facilities in human patients suffering the consequences of congenital or acquired damage to immune facilities. Therefore, the scientific journey that began with an obscure observation aboard a mid-Atlantic fishing boat suddenly opens up new avenues for treating human immune disorders.
Discovery of the immune system can end chronic organ rejection
JB Swann el al., “Immunogenetics of sexual parasitism,” science (2020). science.sciencemag.org/lookup/… 1126 / science.aaz9445
Provided by the Max Planck Institute of Immunobiology and Epigenetics
citation: Immune Functions Traded for Reproductive Success (2020, July 30) Retrieved July 30, 2020 from https://medicalxpress.com/news/2020-07-immune-functions-reproductive-success.html
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