Introduction 
ment of vaccines to limit the spread of HIV. 
Many of us remember how some 30 years ago 
poliomyelitis was to all intents and purposes 
eliminated in this country by the development 
of the Salk and Sabin vaccines, and we are all 
conscious of the fact that many illnesses such as 
measles, rubella, whooping cough, and even 
smallpox have been brought under control. But 
it is still not widely appreciated that the immune 
system is itself subject to a number of serious 
disorders such as lymphoma and leukemia. Our 
Investigators in the Immunology Program 
Alt, Frederick W., Ph.D. 
Atkinson, John P., M.D. 
Bevan, Michael J., Ph.D. 
Bjorkman, Pamela J., Ph.D. 
Bloom, Barry R., Ph.D. 
Bottomly, H. Kim, Ph.D. 
Chaplin, David D., M.D., Ph.D. 
Cooper, Max D., M.D. 
Cress well, Peter, Ph.D. 
Davis, Mark M., Ph.D. 
Fischer Lindahl, Kirsten, Ph.D. 
Flavell, Richard A., Ph.D. 
Ghosh, Sankar, Ph.D. 
Goodnow, Christopher C, B.V.Sc, Ph.D. 
Holers, V. Michael, M.D. 
Jacobs, William R., Jr., Ph.D. 
Janeway, Charles A., Jr., M.D. 
Kappler, John W., Ph.D. 
Neuroscience Program 
Among the most challenging problems in bio- 
medical research are those posed by the human 
brain. How do we perceive the world around us? 
How do we learn from past experiences? How do 
we store and recall information derived from 
those experiences? How do we determine when 
to act and what actions to carry out? What is 
thought? And what are the neural mechanisms 
that underlie language? In a word, how are ail 
those aspects of our lives that most specifically 
define our humanity instantiated in the function- 
ing of our brains? The answers to these questions 
still lie far in the future, but in the past two de- 
cades considerable progress has been made in our 
understanding of some of the cellular and molec- 
ular mechanisms involved in brain function. Rec- 
ognizing this, in 1983 the Institute initiated its 
Neuroscience Program. Until recently, the Neu- 
roscience Program has been largely focused on 
the ways in which nerve cells conduct signals 
ability to deal with these malignant conditions is 
still very limited, but we are beginning to under- 
stand what may cause them. While these dis- 
orders present the most urgent challenges to 
clinical immunology, even relatively minor al- 
lergic disorders continue to pose problems both 
for the practicing physician and for the patients 
who suffer from them. Many of the reports in this 
volume indicate how these and other problems 
associated with the immune system are currently 
being addressed. 
Korsmeyer, Stanley J., M.D. 
Leiden, Jeffrey M., M.D., Ph.D. 
Littman, Dan R., M.D., Ph.D. 
Loh, Dennis Y.-D., M.D. 
Marrack, Philippa, Ph.D. 
Nussenzweig, Michel C, M.D., Ph.D. 
Pay an, Donald G., M.D. 
Perlmutter, Roger M., M.D., Ph.D. 
Peterlin, B. Matija, M.D. 
Schatz, David G., Ph.D. 
Smale, Stephen T., Ph.D. 
Thomas, Matthew L., Ph.D. 
Thompson, Craig B., M.D. 
Tonegawa, Susumu, Ph.D. 
Weiss, Arthur, M.D., Ph.D. 
Weissman, Irving L., M.D. 
Witte, Owen N., M.D. 
and communicate with each other and with the 
effector tissues of the body (such as muscle and 
gland cells) and on the cellular mechanisms in- 
volved in the development of the nervous system. 
Modern neuroscience is founded on two funda- 
mental concepts that derive from the late nine- 
teenth and the early years of the twentieth cen- 
tury. The first of these, commonly referred to as 
the neuron doctrine, is that the fundamental 
functioning units of the nervous system are nerve 
cells, or neurons. Among the cells of the body, 
neurons are distinguished anatomically by the 
fact that they all extend processes (some of con- 
siderable length) that are of two general types: 
shorter tapering processes (dendrites) that 
mainly serve to receive information from other 
cells, and longer processes (axons), of more un- 
iform diameter, that serve to transmit information 
to other parts of the nervous system or to the body 
at large. The second basic concept is that infor- 
liv 
