Vertebrate immunity has been almost revealed completely, but comprehension on invertebrate still lacks behind. Understanding the mechanism of how invertebrate modulate their immune system actually is one of the key for tackling biological problems caused by invertebrate such as hemorrhagic fever by DNEV or malaria due to Anopheles mosquito. In addition, several species of invertebrate such as shrimp have been farmed for consumption or commercial purpose. By enhancing the immune system, it seems possible that the yield is also able to be increased even more. In this short essay, I will elucidate the unique characteristic of vertebrate-less animal that differentiate this group of animals from vertebrate.
The most important aspect that makes the invertebrate immunity unique is that the system do not employ antibody-based defense which in realm of vertebrate this is the stronger defense system created for fighting the pathogen. Invertebrate don’t have common adaptive immunity that underpinning the immune system of higher organism. It means that the organisms lacks of B cell, T cells even the memory cells, thus conventional vaccine used for preventing the viral disease might not work properly if it is given to invertebrate.
Invertebrate primarily relies on innate immunity for their defense. Generally speaking, though this mechanism can be activated directly after pathogen attack, the protection usually isn’t strong enough for complete removal and the specificity absent from the system, which means that the organism treat all pathogen in such similar way. Invertebrate recognizes the pathogen attack after the system encounters specific cellular parts of bacterial or viral such as lipopolysaccharide, peptidoglycan or flaggelin. All of this signal classified as PAMP (Pathogen Associated Molecular Marker) and will be recognized by TLR Receptor and further translated into cellular defense.
Recent finding offers new insight of invertebrate immunity, which it turns out that this sort of animals actually has memory system but it doesn’t based on antibody-system which common among higher organisms. One gene in Drosophila known as DSCAM composed of alternate exon-intron which spliced differently, creating various protein combination which responsible for mediating the defense system for specific organism. Experiment in Drosophila also observes immune priming as second infection of similar pathogen generate stronger immune response, revealing the fact that memory-like immune system also exists in invertebrate, but hasn’t yet completely known.
I found that this last thing quite interesting. Weak adaptive immunity in invertebrate drives the tight association of invertebrate with its beneficial bacterial symbions. In other words, pathogen defense in invertebrate don’t solely come from the organism itself, but also modulated by microbiome community. From evolutionary perspective this makes sense as symbions should provide distinct advantage for its host in order to be stable maintained along generations. If that is not the case, then the symbions will be ditched away from the association as harboring the foreigner internally comes with a fitness cost such as the animals must share the nutrition. Experiment in Drosophila (again) proves this theory as presence of Wolbachia (a type of bacterial endosymbion) makes Drosophila survives better in the times of viral infection. This phenomenon creates selective pressure which favor the symbiosis in the environment where the viral infections are common. The aforementioned fact perhaps answer the reason underlying the finding that insect frequently harboring (exceeding 40% of total species) Wolbachia in their body.