Adopting an orphan

507 suggests that there must be some pathogens that affect both plants and animals. Indeed, one such example is the bacterium Pseudomonas aeruginosa, which attacks both Homo sapiens and Arabidopsis. Perhaps more significant are the common conditions that arise when the immune system malfunctions. There are many known autoimmune diseases in humans, but plants also suffer from them. In lesion mimics, the hypersensitive response that triggers cell death is initiated in the absence of a pathogen. In extreme cases, the whole plant dies from multiple lesions, although this is not a major problem for horticulture or agriculture. The exact mechanisms involved are still unknown, but there is common ground for plant and animal immunologists to study the pathways involved in autoimmune disease, especially where PCD is concerned. Much work still remains to elucidate the immune response in detail, particularly the steps after the pathogen is detected. Nevertheless, cooperation between plant and animal researchers has already yielded important insights into these mechanisms. It is becoming increasingly clear that these two communities, who for so long communicated so little, can pool their resources to investigate immunity.