Advances in immunology.

Much was accomplished in the last decade in understanding how the adaptive immune system evolved to combat pathogens. Essential features of antigen presentation and T lymphocyte recognition were deciphered, setting the stage for further studies that elucidated basic elements of lymphocyte differentiation (including positive and negative selection during lymphocyte ontogeny) and the major interactions that occur among cells in secondary lymphoid organs in an ongoing immune response. The major challenges of today are found in the burgeoning fields of programmed cells death, enzymology of recombination and somatic mutation, development of memory, and the recognition of pathogens by unconventional lymphocytes.