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Division of Rheumatology, Immunology, and Allergy, Department of Medicine, Brigham and Womens Hospital, Boston, MA 02115
LFA-1 exists in a low avidity state on resting leukocytes and is
believed to adopt a high avidity state when the cells are exposed to a
stimulus. Current evidence supports both aggregation of LFA-1 on the
cell surface and conformational changes in the reversible acquisition
of a high avidity state. We studied this regulation by selecting a
Jurkat T cell clone, J-lo1.3, that expresses LFA-1 yet fails to
bind to purified ICAM-1 despite treatment of the cells with PMA or
Mn2+. Several lines of evidence demonstrated the absence of
any changes within LFA-1 itself. LFA-1 protein purified from the
J-lo1.3 clone and the wild-type Jurkat clone, Jn.9, were found to be
functionally equivalent. The cDNA sequences encoding the LFA-1
- and
-chains from J-lo1.3 were identical with the published sequences
except for nine base pairs. However, these differences were also found
in a Jurkat mutant with a constitutively avid phenotype,
J+hi1.19 or the wild-type Jn.9 genomic or cDNA. Fusion of
J-lo1.3 with Jn.9 yielded hybrids that exhibited the J-lo1.3 adhesion
phenotype, which indicated a dominant mutation in J-lo1.3. This
phenotype was relatively specific for LFA-1 among all integrins
expressed by Jurkat. Interestingly, the J-lo1.3 cells had a 1.2-fold
faster doubling time than did the Jn.9 cells. Reversion of J-lo1.3 to
the wild-type adhesion phenotype by mutagenesis and selection also
decreased the growth rate. These data support a connection between
cellular growth and cellular adhesion in
lymphocytes.
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