Influence of arthritis-related protein (BBF01) on infectivity of Borrelia burgdorferi B31

Abstract

Background: Lyme borreliosis, caused by tick-borne Borrelia burgdorferi, is a multi-phasic, multi-system disease in humans. Similar to humans, C3H mice develop arthritis and carditis, with resolution and periodic bouts of recurrence over the course of persistent infection. Borrelia burgdorferi arthritis-related protein (Arp/BBF01), a highly conserved protein among B. burgdorferi s.s. isolates, has been shown to be antigenic in humans with Lyme borreliosis, and a target for antibody-mediated disease resolution in the mouse model.

Results: A mutant strain of B. burgdorferi s.s. deficient of the arp gene and a complemented version of that mutant were created and examined for phenotypic effects in mice compared to wild-type B. burgdorferi. Deletion of arp did not abolish infectivity, but did result in a higher infectious dose compared to wild-type B. burgdorferi, which was restored by complementation. Spirochete burdens in tissues of C3H-scid mice were lower when infected with the arp mutant, compared to wild-type, but arthritis was equally severe. Spirochete burdens were also lower in C3H mice infected with the arp mutant, but disease was markedly reduced. Ticks that fed upon infected C3H mice were able to acquire infection with both wild-type and arp mutant spirochetes. Arp mutant spirochetes were marginally able to be transmitted to naïve hosts by infected ticks.

Conclusion: These results indicated that deletion of BBF01/arp did not abrogate, but diminished infectivity and limited spirochete burdens in tissues of both immunocompetent and immunodeficient hosts, and attenuated, but did not abolish the ability of ticks to acquire or transmit infection.

Figure 1

Borrelia burgdorferi flaB DNA copies per mg tissue weight (means ± standard deviations) in subinoculation site (subIN), heart base (HB), ventricular muscle (VM), quadriceps muscle (Quad) and tibiotarsus (Tibio) from 4 C3H-scid mice inoculated with wild-type (white bars) compared to 5 C3H-scid mice inoculated with arp null Δarp3 B. burgdorferi (black bars). (*, P ≤ 0.05).

Figure 2

Borrelia burgdorferi flaB DNA copies per mg tissue weight (means ± standard deviations) in PCR-positive tissues summarized in Tables 2 and 3, including sub-inoculation site (subIN), heart base (HB), ventricular muscle (VM), quadriceps muscle (Quad) and tibiotarsus (Tibio) from C3H mice inoculated with wild-type (white bars) compared to arp null Δarp3 B. burgdoferi (black bars) at day 14 (a), day 28 (b) and day 42 (c) of infection. (*, P ≤ 0.05) ND: not determined.

Figure 3

Borrelia burgdorferi flaB DNA copies per mg tissue weight (means ± standard deviations) in PCR-positive tissues, including ear, heart base (HB), ventricular muscle (VM), quadriceps muscle (QM) and tibiotarsus (Tt) of mice at 3 weeks after feeding of nymphal ticks from tick cohorts infected with wild-type or arp null Δarp3 B. burgdoferi.