The TEPC 15 (T15) clonotype. a putatively germline antibody specificity, does not appear in the neonatal B-cell repertoire until approximately 1 wk of age. This report extends this observation by the demonstration that: (a) the T15 clonotype follows similar kinetics of appearance in germfree as well as conventionally-reared mice; (b) maternal influences and genetic background play a minor role in the development of the T15 clonotype since CBF 1 neonates raised by C57BL/6 or BALB/c mothers acquire the T15 clonotype at the same time in ontogeny as BALB/c neonates; (c) the lack of phosphorylcholine (PC)-specific B cells shortly after birth is reflected in a death of PC-binding cells in the neonate as well; and (d) no PC-specific B cells are found in 19-day fetal liver or in bone marrow until 7 days of life, coincident with their appearance in the spleen. These findings, along with a previous report that PC-specific splenic B cells are tolerated as late as day 10 after birth, confirm the invariant, late occurrence of the T15 clonotype and support a highly-ordered, rigorously predetermined mechanism for the acquisition of the B-cell repetoire. The results are discussed in light of other studies on the ontogeny of B-cell specificity and in terms of the implications on the mechanism by which antibody diversity is generated.
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