ORAL DELIVERY OF PURIFIED LIPOPROTEIN OSPA PROTECTS MICE FROM SYSTEMIC INFECTION WITH BORRELIA-BURGDORFERI

The lipoprotein outer surface protein A (OspA) of the Lyme disease age nt, Borrelia burgdorferi, has provided protection to mice and other an imals against systemic infection when delivered orally as a recombinan t protein in Escherichia coli, bacille Calmette-Guerin or Salmonella t yphimurium. In the present study purified recombinant strain B31 OspA or outer surface protein D (OspD), another lipoprotein of B. burgdorfe ri, were administered either subcutaneously (s.c.) or orally without c ell carrier or adjuvant to mice. In comparison to the OspD preparation , the OspA protein was 256-fold more resistant to trypsin. Whereas Osp A in the suspension was in regular complexes of 17-25 nm in size, OspD formed amorphous globules of different sizes. Animals received a prim ary immunization and at least one booster. Mice immunized s.c. with ei ther OspA or OspD had detectable antibodies to B. burgdorferi by enzym e-linked immunosorbent assay (ELISA), growth inhibition assay (GIA) an d immunoblot. Delivered orally, OspA but not OspD elicited a specific antibody response, including IgA, as determined by these assays. The g eometric mean titre of sera from mice who received 4 mu g of OspA oral ly on days 1, 2, 4, 21 and 22 was 1470 by Ig ELISA, 320 by IgA ELISA a nd 128 by GIA. In infectious challenge experiments with B. burgdorferi strain Sh2-2-82 (OspA(+)OspD(-)) inoculated intradermally at 100 x th e ID50, all eight mice immunized with the 4 mu g dose of OspA were pro tected; none of the mice immunized with the 4 mu g dose of OspD were p rotected (P<0.001 by Fisher exact test). These studies indicate that t he lipoprotein OspA provides protectin against systemic B. burgdorferi infection when delivered orally as a purified protein. (C) 1997 Elsev ier Science Ltd.