Evidence that the BBA68 Protein (BbCRASP-1) of the Lyme Disease Spirochetes Does Not Contribute to Factor H-Mediated Immune Evasion in Humans and Other Animals

Abstract

BBA68 (BbCRASP-1) of the Lyme disease spirochetes binds human factor H (FH) and FH-like protein 1 (FHL-1).Here we assess transcription of the BBA68 gene and production of BBA68 in infected mice and humans using real-time reverse transcriptase PCR and immunoblotting. The species specificity of FH binding to BBA68 was also tested. The data suggest that BBA68 does not play an important role in immune evasion in animals.The Lyme disease spirochete, Borrelia burgdorferi, can bind the human complement regulatory proteins, factor H (FH) and FH-like protein 1 (FHL-1) (1,8,11,16). FH and FHL-1 serve as cofactors in the factor I-mediated cleavage of C3b (18). C3b is an important opsonin and central component of the complement system. The binding of FH and FHL-1 to the bacterial surface is thought to locally increase the efficiency of C3b cleavage, locally downregulate the alternative complement cascade, and inhibit C3b-mediated opsonophagocytosis (30). The FH/FHL-1 binding proteins (FHBPs) identified in B. burgdorferi B31MI include the OspE proteins (BBL39, BBN38, and BBP38) and BBA68 (also referred to as BbCRASP-1) (1,8,10,11,15,16). Analyses of in vitro-cultivated bacteria indicate that BBA68 is the dominant FHBP and is the only paralog of the 14-member protein family 54 (The Institute for Genome Research designation) to exhibit human FH/FHL-1 binding activity (10, 15). Inactivation of BBA68 increases sensitivity to complement in vitro, and the introduction of BBA68 into Borrelia garinii strains that lack the gene decreases their serum sensitivity (3). While it is widely held that BBA68 plays an important role in immune evasion, earlier studies provided evidence that it may not be expressed during infection (2,17,23,25). In fact, Tokarz et al. demonstrated that, when human blood was added to actively growing cultures, BBA68 and BBA69 gene transcription was downregulated 1.8-fold. In addition, Brooks et al. demonstrated a sevenfold reduction in BBA68 transcript levels in spirochetes cultivated in dialysis membrane chambers implanted into the peritoneal cavities of rats (2, 23). The goals of this study were to further investigate the putative contribution of BBA68 in immune evasion in humans and other animals. In summary, the data indicate that the BBA68 gene is not transcribed during infection in mice and does not elicit an antibody response in mice and humans. In addition, BBA68 does not bind to FH produced by animals other than humans, and hence it is not likely to be involved in FH-mediated immune evasion in its natural mammalian reservoirs. Collectively, the data suggest that BBA68 does not carry out an important function directly in infected humans and animals.As one approach to assessing production of BBA68 during infection we screened for an antibody response to BBA68 in infected mice and humans. Since an understanding of the potential heterogeneity of BBA68 is an essential first step in interpreting immunoblot analyses and identifying the appropriate test antigen to be employed in the screening, we first assessed...

Borrelia burgdorferi complement regulator-acquiring surface proteins (BbCRASPs): Expression patterns during the mammal–tick infection cycle

“…In contrast, cspA transcripts become undetectable within two weeks of establishing mammalian infection Lederer et al, 2005;McDowell et al, 2006;Bykowski et al, 2007). Humans and laboratory mice produce limited antibody responses to BbCRASP-1, consistent with brief exposure of that protein to host immune systems .…”

Delineation of Species-Specific Binding Properties of the CspZ Protein (BBH06) of Lyme Disease Spirochetes: Evidence for New Contributions to the Pathogenesis of Borrelia spp

“…B. afzelii and B. garinii, which are generally more sensitive to complement (5,20,40), produce fewer FHBPs. Some FHBP-encoding genes are environmentally regulated (10,26,31,39), and the proteins they encode have been shown to have differing binding specificities for members of the FH protein family (19,24,34). Recent work has demonstrated that FHBPs can also bind to a series of serum proteins (16,26,35).…”

Selective Binding of Borrelia burgdorferi OspE Paralogs to Factor H and Serum Proteins from Diverse Animals: Possible Expansion of the Role of OspE in Lyme Disease Pathogenesis

“…One or more OspE paralogs have been demonstrated to be expressed during infection in ticks and mammals, indicating that they may carry out important functions in these environments (16-18, 20, 32-34, 38). Interestingly, while BBA68 has clear factor H/FHL-1 binding ability, it is not expressed during infection; thus, its role in pathogenesis is unclear (6,26,42,43).…”