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Brandeis University, Rosenstiel Research Center, Waltham, MA 02454
Several mechanisms that diversify the adult immune repertoire, such
as terminal deoxynucleotidyl transferase-dependent N region addition,
are not available to the neonatal mouse. One important process that
contributes to protective immunity in the adult is somatic mutation,
which plays a major role in the generation of high affinity memory B
cells. It is not clear whether B cells in the neonatal mouse can
activate the somatic mutation machinery. To investigate this, we
immunized neonates with
poly(L-Tyr,L-Glu)-poly-D,
L-Alapoly-L-Lys complexed with methylated
BSA, or (4-hydroxy-3-nitrophenyl)acetyl coupled to chicken
-globulin. Eight to fourteen days after priming, V(D)J
rearrangements of known VH genes (VHSM7 family)
were screened for mutations using a temperature-melt hybridization
assay and oligonucleotide probes specific for
complementarity-determining regions I and II; possible mutations were
confirmed by sequence analysis. More mutations per sequence were found
in heavy chains from neonates immunized with
(4-hydroxy-3-nitrophenyl)acetyl coupled to chicken
-globulin than in
those from neonates immunized with poly(L-Tyr,
L-Glu)-poly-D,L-Ala-poly-L-Lys
complexed with methylated BSA. Mutations were found in heavy chains
lacking N regions, suggesting that B cells of the putative fetal
lineage can somatically mutate and diversify an initially limited
repertoire. Since neonates immunized as early as 1 or 2 days after
birth had mutations, the somatic mutation machinery can be activated
soon after birth, suggesting that early vaccination should result in
affinity maturation and protective immunity in the
neonate.
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C. N. Jenne, L. J. Kennedy, P. McCullagh, and J. D. Reynolds A New Model of Sheep Ig Diversification: Shifting the Emphasis Toward Combinatorial Mechanisms and Away from Hypermutation J. Immunol., April 1, 2003; 170(7): 3739 - 3750. [Abstract] [Full Text] [PDF] |
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