Microbes have many mechanisms for defense and attack, but not identical to mammalian immune systems as we traditionally think of. But there are general similarities....for example we have innate and adaptive immune responses, and so do bacteria. They have innate defenses or immune tools such as physical barriers and chemicals (just not immune cells), and they have adaptive immune responses such as the CRISPR mechanism for recognizing and remembering foreign invaders (antigens).

Insects also have innate and adaptive immune tools, and have a hemolymph comprised of hemocytic cells like plasmatocytes (similar to our phagocytic macrophages) and a few crystal cells (for storage of antimicrobial particles) and lamellocytes (for dealing with larger microbes). None of these cell types though can undergo DNA rearrangement and somatic hypermutation to generate a cell type with immunological memory, as is the case with their mammalian counterparts. So it depends on what you mean by lowest life from with the highest complexity immune system because many of these systems are complex in their own right but yet simply effective also in their own evolutionary way. Strictly speaking, insects don't get GVHD which is a complication of transplanted tissue from a genetically different donor, and part of the mechanism of chronic GVHD involves B-cells and antibody production among other immune responses. But insect immunity can recognize other cells or antigens as foreign, and hemocyte-mediated responses are regulated by signaling factors and effector molecules that control cell adhesion and cytotoxicity. Many lines of evidence indicate that humoral and cellular defense responses are well-coordinated and that there is cross-talk between the immune and nervous system in regulating inflammatory-like responses in insects during infection or foreign invasion.

Although microbes are small microorganisms, they are so smart. They can set different mechanisms to develop resistance against the unwanted effects of intrinsic and extrinsic factors. For example, bacteria form spores to protect themselves from unsuitable conditions. They express antibiotic resistant genes to withstand the antimicrobial activity of antibiotics. Fungi can do the same.

Insects have also used different strategies to prevent themselves from their enemies. I think these struggles can be compared with the immune system of mammals as far as the ultimate goal seems more or less the same, which is basically defending the host. 

Hi

this subject that you said is related to quorum sensing of bacteria.

bacteria by sensing changes in their environment response to changes and their response depends on factors that caused change and ability of bacteria by their genes.  

Microbes have many mechanisms for defense and attack, but not identical to mammalian immune systems as we traditionally think of. But there are general similarities....for example we have innate and adaptive immune responses, and so do bacteria. They have innate defenses or immune tools such as physical barriers and chemicals (just not immune cells), and they have adaptive immune responses such as the CRISPR mechanism for recognizing and remembering foreign invaders (antigens).

Insects also have innate and adaptive immune tools, and have a hemolymph comprised of hemocytic cells like plasmatocytes (similar to our phagocytic macrophages) and a few crystal cells (for storage of antimicrobial particles) and lamellocytes (for dealing with larger microbes). None of these cell types though can undergo DNA rearrangement and somatic hypermutation to generate a cell type with immunological memory, as is the case with their mammalian counterparts. So it depends on what you mean by lowest life from with the highest complexity immune system because many of these systems are complex in their own right but yet simply effective also in their own evolutionary way. Strictly speaking, insects don't get GVHD which is a complication of transplanted tissue from a genetically different donor, and part of the mechanism of chronic GVHD involves B-cells and antibody production among other immune responses. But insect immunity can recognize other cells or antigens as foreign, and hemocyte-mediated responses are regulated by signaling factors and effector molecules that control cell adhesion and cytotoxicity. Many lines of evidence indicate that humoral and cellular defense responses are well-coordinated and that there is cross-talk between the immune and nervous system in regulating inflammatory-like responses in insects during infection or foreign invasion.

Thanks, Dr. Sedghizadeh, thats what i was looking for. Anyone interested in learning more I found the following papers to be pretty good start:

"Mosquito hemocyte-mediated immune responses"- Hillyer and Strand (2014)

"The insect cellular immune response"- Michael R. Strand (2008)

What about plant immune system, poorly understood but------?

The plant immune system . . . (Fig. 1).

Article Pivoting the Plant Immune System from Dissection to Deployment