Ly-6 genes are being analyzed to determine the na- 
ture of the expressed gene. Other investigators 
have shown aberrant Ly-6C expression in T cells 
from NOD pancreatic islets. 
III. Analysis of the Development of an Antibody 
Response. 
The cellular basis for heterogeneity in the sec- 
ondary immune response was studied earlier by 
creating a large set of B cell hybridomas from a sin- 
gle C57BL/6 mouse immunized with the hapten NP 
coupled to chicken gamma globulin. Individual 
progenitor cells were identified by the uniqueness 
of the DNA sequences of the heavy- and light-chain 
joining regions, which are established early in the 
life of a B cell. The hybridomas were also used to 
characterize somatic mutation, affinity, and the 
presence of certain antigenic determinants on these 
antibodies. The results demonstrated the extreme 
oligoclonality in the normal secondary response 
and suggested that the oligoclonality seen in the 
secondary immune response would also be seen in 
the primary immune response to NP. 
Evidence for oligoclonality was found in the pri- 
mary anti-NP response, but the analysis of the ex- 
pressed sequences revealed much more about the 
early events in memory formation. At day 12, there 
were seven predominant clones detected. Three of 
these clones expressed the prototype Ig gene com- 
binations. Surprisingly, all members of a family ex- 
PUBLICATIONS 
pressed the same heavy-chain isotype and pos- 
sessed only common somatic point mutations. For 
the prototype combination, the most common sin- 
gle point mutation that creates a 10-fold higher 
affinity antibody was observed in two of three 
families. 
These results reveal the characteristics of the 
onset and development of memory B cells. For the 
first time it is possible to develop a model for this 
process. The strength of the response, in part due 
to the affinity of the germline-encoded antibodies, 
has revealed the affinity threshold for selection of 
these antibodies. Once a successful mutation oc- 
curs in this response, a single memory B cell must 
differentiate into a plasma cell. It then either re- 
duces considerably or terminates the occurrence of 
additional somatic mutation. The resultant expan- 
sion of the plasma cell lineage generates a wave of 
B cells that are seen as a family of related antibod- 
ies. The mutational mechanism must initiate early, 
probably by day 3-4, and is a continuous process 
in memory cells. The original germline sequence is 
not maintained, because increases in affinity are se- 
lected. In this response, additional mutations must 
gradually accumulate, because by three weeks con- 
siderably more mutations are evident. 
Dr. Bothwell is also Associate Professor of Im- 
munobiology and Biology at Yale University School 
of Medicine. 
Articles 
Ballard, D.W, Philbrick, WM., and Bothwell, A.L.M. 1988. Identification of a novel 9-kDa polypeptide from 
nuclear extracts. DNA binding properties, primary structure, and in vitro expression. / Biol Chem 
263:8450-8457. 
Blier, PR., and Bothwell, A.L.M. 1988. The immune response to the hapten NP in C57BL/6 mice: insights into 
the structure of the B-cell repertoire. Immunol Rev 105:27-43. 
Bothwell, A., Pace, P.E., and LeClair, K.R 1988. Isolation and expression of an IFN-responsive Ly-6C chromo- 
somal gene. J Immunol 140:2815-2820. 
LeClair, K.P, Bridgett, M.M. , Dumont, F.J., Palfree, R.G.E., Hammerling, U., and Bothwell, A.L.M. 1989. Kinetic 
analysis of Ly-6 gene induction in a T lymphoma by interferons and interleukin 1, and demonstration of 
Ly-6 inducibility in diverse cell types. Eur J Immunol 19:1233-1239. 
Marion, T.N., Bothwell, A.L.M., Briles, D.E., andjaneway C.A., Jr. 1989. IgG anti-DNA autoantibodies within 
an individual autoimmune mouse are the products of clonal selection. J Immunol 142:4269-4274. 
Su, B., and Bothwell, A.L.M. 1989. Biosynthesis of a phosphatidylinositol-glycan-linked membrane protein: 
signals for posttranslational processing of the Ly-6E antigen. Mol Cell Biol 9:3369-3376. 
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