IMMUNOGLOBULIN SWITCH CIRCULAR DNA IN THE MOUSE INFECTED WITH NIPPOSTRONGYLUS-BRASILIENSIS - EVIDENCE FOR SUCCESSIVE CLASS SWITCHING FROM MU TO EPSILON VIA GAMMA-1

We have characterized immunoglobulin switch circular DNA in mice infected with the nematode parasite Nippostrongylus brasiliensis. Two kinds of circular DNA were identified in the lymph nodes as excision products of switch recombination of immunoglobulin heavy-chain constant region (C(H)) genes. One is a recombinant between C(μ) and C(γ1) (γ1 circle), and the other is a recombinant between C(γ1) and C(ε) (ε circle). In the ε circle, a short piece of switch μ (S(μ)) sequence was inserted between S(ε) and S(γ1) sequences. The inserted S(μ) sequence could be a trace of the preceding switch from C(μ) to C(γ1). These findings indicate that parasitic infection can induce class switch recombinations in a successive manner, first from C(μ) to C(γ1), and then from C(γ1) to C(ε).