Thus, fish are called poikilothermic. Macrophages develop from bone marrow precursors which mature and enter the bloodstream as monocytes. Macrophages secrete signalling molecules called cytokines and chemokines which orchestrate the immune response. Cytokines are small proteins which allow cells of the immune system to communicate with one another via cytokine receptors expressed at the cell surface. Some cells can take up small particulate matter by surrounding the particle with extrusions of the cell membrane by a process termed phagocytosis.
Macrophages have great phagocytosis ability.
Macrophages in culture will phagocytose a whole range of different particles from small latex beads to polymer beads twice their own diameter.