Re: How do the infection fighting cells of other species compare to those of humans?

John,

The immune cells of most species of animals are not well studied. 
The exception is the mouse, which has been extensively studied. 
Similar cell types, receptor molecules, and molecular signaling 
pathways exist in both humans and mice. It is likely that the immune 
systems of other mammals are similar to those of humans.

Birds have a cellular immune system that is similar to mammals, 
with some notable differences. However, invertebrates lack 
antibody-producing cells or even lymphocytes, which confer 
specificity to immune reactions. Reponse to infection is conferred by 
cells and peptides that react to "abnormal" conditions.

In general, one can say that the complexity and specificity of the 
immune systems of different animals is related to the complexity of 
the animal itself.