Origin of immunity: protozoa. Dissemination 51st
Protozoa are unicellular microorganisms that, from the immunitary point of view, present a primitive immunitary defense line based on the cellular membrane. This membrane is composed of a phospholipides double layer, crossed by globular protein formations whose function is the exchange of nutrients with the outside. On protozoa cellular membrane surface we can find glycolipids formations (oligosaccharides) whose mission is to detect external attacks and to mobilise calcium reserves of the protozoa, in order to neutralize external agents. Some authors have described that another primitive defense mechanism like melanin production, defense against solar rays, can be adopted by unicellular microorganisms as a defense process against biological attacks, as melanin has a certain toxicity grade against microbial agents.
In summary, the immunitary system of unicellular microorganisms presents:
1. Barrier mechanism by the cellular membrane.
2. Chemical neutralization mechanism by stores of calcium mobilisation.
3. Defense mechanism by synthesis of substances which are toxic for the microorganisms (like melanin).
These mechanisms do not disappear in more complex animals, thus each new evolutive step incorporates new mechanisms mantaining the previous ones. It is known the injuries calcification process in birds and mammals organs, which origin must be searched in the neutralization mechanisms of unicellular microorganisms, as well as injuries melanin pigmentation, which origin can be found in melanin production, for protection against solar rays, later adapted to defense against biological attacks, in unicellular microorganisms.