Expression and immunological analysis of the plasmid-Borne mlp genes of Borrelia burgdorferi strain B31

A lipoprotein gene family first identified in Borrelia burgdorferi strain 2 97, designated 2.9 LP and recently renamed mlp, was found on circular and l inear plasmids in the genome sequence of B. burgdorferi strain B31-M1. Sequ ence analyses of the B31 mlp genes and physically linked variant gene famil ies indicated that mlp gene heterogeneity is unique and unrelated to locati on or linkage to divergent sequences. Evidence of recombination between B31 mlp alleles was also detected. Northern blot analysis of cultured strain B 31 indicated that the mlp genes were not expressed at a temperature (23 deg rees C) characteristic of that of ticks in the environment. In striking con trast, expression of many mlp genes increased substantially when strain B31 was shifted to 35 degrees C, a temperature change mimicking that occurring in the natural transmission cycle of the spirochete from tick to mammal. P rimer extension analysis of the mlp mRNA transcripts suggested that sigma 7 0-like promoters are involved in mlp expression during temperature shift co nditions. Antibodies were made against strain B31 Mlp proteins within the f irst 4 weeks after experimental mouse infection. Importantly, Lyme disease patients also had serum antibodies reactive with purified recombinant Mlp p roteins from strain B31, a result indicating that humans are exposed to Mlp proteins during infection. Taken together, the data indicate that strain B 31 mlp genes encode a diverse array of lipoproteins which may participate i n early infection processes in the mammalian host.