Login

Join for Free!
122499 members
Advertisement
Advertisement

table of contents table of contents

One of the biggest threats to survival is infection, so that the …


Home » Biology Articles » Evolutionary Biology » Auto-immunity as Evolutionary by Product of Adoptive Immunity and Source ofAnti-tumor Immunity Failure » Evolution of the Vertebrate Immune System

Evolution of the Vertebrate Immune System
- Auto-immunity as Evolutionary by Product of Adoptive Immunity and Source ofAnti-tumor Immunity Failure

Some evolutionary processes can be studied directly, while the evolution of the immune system and immunity cannot. The evolution of immunity is a macro-evolutionary process, which can be studied by examining the patterns in biological populations or species of related organisms and inferring process from pattern. One of the possible ways to carry out a detailed investigation into the issue of the evolution of the immune system is virtually by comparing the characteristics of the immune system across species and classes. In addition, the determination of the genes and molecules conserved throughout evolution is helpful in identifying the mechanisms of the immune system evolution, while variable genes as well as the emergence of new genes along evolution enable the identification of various evolutionary pressures, their duration and strength. This provides a better understanding of how the immune system works under physiological and pathological conditions. This approach, however, is not an easy one since only few percent of the total number of species that have inhabited the planet to date are available for research. Notwithstanding this limiting factor, previous studies have produced sufficient findings for the construction of a hypothetical model of the evolution of the immune system in vertebrates, and also cleared the pathway towards reaching further relevant presumptions and conclusions.

The evolution of the immune system is a direct consequence of microbes-exerted selection pressure on multicellular organisms. The vertebrate immune system was to some extent inherited from invertebrates, whereas a part of it has advanced considerably in the course of its own evolution. Although certain vertebrate-specific properties such as immune recognition and immune memory have also been identified in invertebrates in rudimentary forms, it is particularly those qualities like progressive development of humoral and cellular adoptive immunity, Major Histocompatibility Complex (MHC), variable class I and class II genes, precise mechanisms of immune recognition and long-term immune memory that reflect the fundamental evolutionary advancement of the vertebrate immune system.

The presumption that auto-immunity could have represented evolutionary new forms of strong selection pressure closely associated with the evolution of the mammalian immune system correlates with the unique control mechanisms of immune response verified in this vertebrate. In short, the evolution of the mammalian immune system has possibly undergone the pressures of at least four quite diverse factors: microbes, auto-immunity, alloimmunity/reproductive efficacy and tumors. However, there is opinion that auto-immunity and tumors cannot be sources of strong selection pressures, as most of these generally occur after leaving offspring. On the contrary, alloimmunity/reproductive efficacy might have been the source of a very strong selection pressure that greatly influenced the evolution of the mammalian immune system.

The possible effects of such heterogeneous and complex evolutionary pressures are the evolutionary development of the mammalian immune system into one of the most complex, most organized and multilevel controlled system in the world of living beings. Notwithstanding the possibility that auto-immunity might be the by-product of the evolution of adoptive immunity, this phenomenon could have been one of the factors significantly influencing the course of the evolution of vertebrate immune system and development of the mechanisms for the control of immune reaction. The evolutionary modelling of the vertebrate immune system under the influence of microbes and auto-immunity, did not probably result in the weakening of the killer mechanisms efficacy and MHC genes variability, but could have been followed by the introduction and co-evolution of evolutionary new mechanisms for the control of immune reaction, that could have restrained the potentially "self-destructive" power of the adoptive immunity.

1. The evolution of the vertebrate immune system from cartilagofish to mammals is characterized by several processes featuring clearly perceivable evolutionary trends (1):
2. The grouping and clustering of MHC genes;
3. Associating of TAP/LMP genes with a less variable class of MHC genes (class I in fishes and class II in mammals);
4. The emergence of auto-immunity like a form of selection pressure;
5. The sophisticated mechanisms of "self"-tolerance mechanisms;
6. The sophisticated mechanisms of immune reaction control mediated by cells of innate immune system;
7. The increasing of the number of the immune cell subtypes involved in the control of immune reaction (Th1, Th2, APCs, DCs);
8. The regulation of immunoreactivity mediated by sex hormones;
9. The increasing of the number of cytokines;
10. The regulation of immunoreactivity mediated by a complex cytokine network;

These phenomena could be associated with a better and more precise control of the immune reaction. However, it is very difficult to answer the question how big the contribution of the selection pressure of auto-immunity on the evolutionary development of the vertebrate immune system is. Judging from the pathogenesis of auto-immune diseases which are clearly associated with the basic features of the adoptive immunity like MHC, and also from the high incidence of auto-immune diseases in mammals, this phenomenon could be a significant factor of the selection pressure and evolutionary modelling, and permanent re-modelling, of the vertebrate immune system and their control mechanisms.


rating: 4.09 from 11 votes | updated on: 2 Mar 2009 | views: 27160 |

Rate article:







excellent!bad…