ABSTRACT
Even primitive organisms possess mechanisms for defending themselves from microbial attack. In fact, it was the phagocytic cells of starfish which gave Metchnikoff the inspiration for the cellular theory of immunity a century ago. In this discussion, we will divide non-specific immune processes into four broad categories: constitutional resistance; means for preventing entry of microorganisms into the body; humoral factors which kill or inhibit the growth of pathogens; and cells which ingest and destroy microbes.
