Prolonged adjuvant stimulation in germ-free BALB-c mice: development of plasma cell neoplasia.

BALB/c mice develop a high incidence (60–80 per cent) of plasma cell tumour (PCT) following the introduction of mineral oil (MO) into the peritoneal cavity. Germ-free (GF) mice have a less developed lymphoreticular system, including a decreased number of plasma cells, than their conventional (CONV) counterparts. When GF BALB/c mice were injected i.p. with mineral oil they failed to develop the expected incidence of PCT. Only two of thirty-three GF mice (6 per cent) developed PCT, while twenty-four of thirty-one ex-GF (77 per cent) and twenty-eight of forty CONV BALB/c (70 per cent) developed PCT. The ex-GF and CONV mice had average times for PCT diagnosis of 11.3 and 11.5 months, but both GF tumours were discovered 18 months after mineral oil injection. Three groups of GF mice received three different sterile protein antigens along with MO and no PCT developed in these mice; in the GF group receiving MO alone, both PCT arose. The GF mice in this experiment did develop a high incidence (80 per cent) of lymphoreticular neoplasms of a type more primitive than PCT. This experiment suggests the importance of microbial flora in the development and differentiation of the plasma cells which respond to a carcinogenic stimulus in a genetically susceptible host.