Evolution of innate and adaptive immunity: can we draw a line?

Several recent findings in the field of comparative immunology have reinforced the importance of examining the molecular and functional features of immune systems in a variety of organisms. Particularly exciting are the discoveries of a new gene rearrangement mechanism in lampreys and a somatic diversification of mollusk immune genes. These immune features being found in animals previously believed only to have innate immunity, as well as the flood of information on immune genes, molecules and mechanisms in many different creatures, have prompted us to revisit the artificial dichotomy between adaptive and innate immune systems. Although we draw no startling conclusions, we hope to encourage different thought patterns when viewing immune systems.