Table 1.

Allelic methylation of the κ gene in single cells

Cells with monoallelic PCR product
κ+ B cells		Nonlymphoid cells
(+AvaI)	(−AvaI)	(+AvaI)
89/103 (86%)	4/12 (33%)	6/39 (15%)

Single-cell PCR using primer sets P1–P4 was carried out as described in Materials and Methods with (+) or without (−) pretreatment with AvaI, and the products were digested with HhaI to determine the contribution of the M. spretus and M. musculus alleles (examples shown in Fig. 2b). It should be noted that the monoallelic products (15%) seen in the nonlymphoid control cells are probably due to inefficient PCR reactions. In the absence of AvaI, B-cell DNA yields a high background level (33%) of monoallelic products primarily because of rearrangements to J4 or J5, which remove the primer sequences.