Sir

Margaret McFall-Ngai's Essay, “Care for the community” (Nature 445, 153; 2007) suggests that the unique existence of immune memory in vertebrates (the 'adaptive' immune system) could have evolved to recognize and manage beneficial microbe communities that invertebrates usually don't use.

This hypothesis is interesting and deserves consideration, although I would like to bring readers' attention to some earlier research, for example by J. Kurtz and K. Franz (Nature 425, 37–38; 2003), mostly by evolutionary ecologists, reporting immune memory in invertebrates.

The vertebrate immune memory is based on immunoglobulins that invertebrates lack. To date, we know almost nothing of immune-memory mechanisms in invertebrates; hence the phenomenon has been observed before being mechanically understood. It is the opposite of the current trend in which genes are discovered before their functions are known, and is a good illustration of the importance of the complementarity of disciplines in biology.

Even so, the role and significance of immune memory in invertebrates remains unknown, and the interesting ideas discussed in this Essay could help to explain why this function might not be as central for invertebrates as it is for vertebrates.