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Natural antibodies are those immunoglobulin molecules found in mammalian serum that arise in the absence of exposure to environmental pathogens and may comprise an early host defense against invading pathogens. The spirochete Borrelia burgdorferi first encounters natural antibodies when its arthropod vector, Ixodes scapularis, begins feeding on a mammalian host. Natural antibodies may therefore have an impact on pathogens within blood-sucking vectors, prior to pathogen transmission to the mammal. In this study, we investigated whether natural antibodies influenced the number and/or phenotype of B. burgdorferi organisms within feeding I. scapularis nymphs. Using a competitive PCR, we found that ticks ingesting a blood meal from B-cell-deficient mice, which lack all immunoglobulins, contained fivefold more spirochete DNA than ticks feeding on control mice. Spirochete DNA levels could be reduced to that of controls with passive transfer of normal mouse serum or polyclonal immunoglobulin M (IgM), but not IgG, into B-cell-deficient mice prior to placement of infected ticks. At 48 h of tick feeding, 90% of spirochetes within salivary glands of ticks removed from B-cell-deficient mice were found by confocal immunofluorescence microscopy to express outer surface protein A (OspA), compared to only 5% of salivary gland spirochetes from ticks detached from control mice. Taken together, these results show that ingestion of natural antibodies limits the spirochete burden within feeding ticks. Because OspA is normally downregulated when spirochetes moved from the tick midgut to the salivary gland, our findings suggest that OspA-expressing midgut spirochetes may be particularly susceptible to the borrelicidal effects of these molecules.

CD1 molecules can present microbial lipid Ag to T cells, suggesting that they participate in host defense against pathogens. In this study, we examined the role of CD1d in resistance to infection with the Lyme disease spirochete, Borrelia burgdorferi (Bb), an organism with proinflammatory lipid Ag. Bb infection of CD1d-deficient (CD1d(-/-)) mouse strains normally resistant to this pathogen resulted in arthritis. Pathology correlated with an increased prevalence of spirochete DNA in tissues and enhanced production of Bb-specific IgG, including IgG to Ag rapidly down-modulated on spirochetes in vivo. CD1d(-/-) mice exhibited high-titer Bb-specific IgG2a, an isotype commonly induced in disease-susceptible mice but not in the disease-resistant control mice in this study. These results show that CD1d deficiency impairs host resistance to a spirochete pathogen, and are the first example of a mutation that imparts Bb-resistant mice with the Ab and disease profile of a susceptible mouse strain.

Autoantibodies directed at a diverse group of proteins of the U1/Sm ribonucleoprotein (snRNP) are characteristic of systemic lupus erythematosus and are found in the MRL murine model of this disease. This study examines the role of transgenic B lymphocytes in the regulation of autoreactive T cells to the snRNP autoantigen. Transgenic mice were developed bearing an Ig heavy chain gene specific for the D protein component of murine snRNP. B lymphocytes in these mice are neither deleted nor anergic and are of an immature (heat-stable Aghigh) phenotype. T lymphocytes from anti-snRNP transgenic mice were examined using a recombinant form of the D protein of the murine snRNP complex. Our results revealed that transgenic anti-snRNP B cell APCs stimulated CD4 T cells from wild-type C57BL/6 and MRL lpr/lpr mice, while nonspecific APCs failed to stimulate CD4 T cells. This study demonstrates that autoreactive T cells are not deleted from wild-type mice, although their activation is facilitated by autoantigen-specific APCs. The snRNP-reactive T cells in C57BL/6 transgenic mice are tolerized, in contrast to those T cells from MRL lpr/lpr transgenic mice. These studies implicate a role for autoreactive B lymphocytes in the in vivo activation and/or diversification of autoreactive T cells.

Transfer of immune serum from immunocompetent mice infected with B. burgdorferi protects mice against syringe challenge, and transfer of immune serum after infection is established induces arthritis resolution but does not clear infection or spirochetemia or resolve carditis. Immune serum had very-high-titer passive protective activity against syringe challenge but failed to protect mice against host-adapted spirochetes when they were challenged with infected tissue transplants. Mice were passively immunized at selected intervals relative to challenge inoculation with antisera to recombinant forms of an immunodominant region of flagellin, P39, and OspC (which are recognized by immune serum), but none provided protection or modified existing infection or disease. Results suggest that spirochetes within joints, but not in other tissues, are selectively vulnerable to immune serum and that immune serum appears to contain antibody against yet-to-be-identified antigens that may be selectively expressed in the context of joint tissue.

Lyme borreliosis in transgenic mice tolerant to Borrelia burgdorferi outer surface protein A (OspA) from the weakly virulent B. burgdorferi 25015 was assessed because the response to OspA has been implicated in protective immunity and is suspected in disease pathogenesis. B. burgdorferi 25015 is infectious but does not cause significant arthritis in C3H/HeN mice. Tolerance of mice to B. burgdorferi N40 OspA had no effect on disease. Since B. burgdorferi N40 is more virulent than and genetically distinct from B. burgdorferi 25015, the generality of these findings was investigated. OspA-25015-transgenic mice were tolerant to OspA-25015 and did not develop OspA antibodies or cellular responses following immunization with OspA-25015. The development and resolution of Lyme arthritis was similar in transgenic and nontransgenic littermates, suggesting that ablation of the OspA-25015 response does not cause B. burgdorferi 25015 to become more arthritogenic.

Objective: To characterize the serologic responses of dogs naturally exposed to or vaccinated against Borrelia burgdorferi and to assess responses at intervals after antibiotic treatment., Design: Prospective, controlled clinical trial., Animals: 19 dogs of various breeds and ages with narrowly defined clinical criteria of limb/joint borreliosis and 10 control dogs of equivalent age were used to determine serologic responses following natural exposure to the organism. Eight seronegative dogs were used to determine serologic responses following vaccination., Procedure: Serologic responses to B burgdorferi and recombinant outer surface protein (Osp)A, flagellin, and P39 were assessed by means of ELISA and western immunoblot. Passive protective activity was assessed by use of a mouse protection assay., Results: Naturally exposed dogs were seropositive, but had variable ELISA titers and immunoblot profiles. Immunoblot analysis did reveal consistent reactions to flagellin, P39, and a 22 kd protein, but not to OspA. Antibody responses did not change appreciably up to 13 weeks after antibiotic treatment. Vaccinated dogs had strong reactions to OspA and OspB, but not to P39., Clinical Implications: Dogs with clinical borreliosis are seropositive and remain seropositive after antibiotic treatment, emphasizing that serologic testing is not a useful means of measuring clinical response. Serologic responses of infected dogs can be discriminated from those of vaccinated dogs by means of immunoblot analysis, and recombinant P39 is a potentially useful antigen for that purpose.

The events involved in T cell activation are initiated at the cell surface by the interaction of ligands with specific cell surface receptors on the T cell. Central to antigen-induced activation is the CD3/Ti complex, a complex multi-chain receptor responsible for antigen/MHC recognition and signal transduction. Triggering the CD3/Ti complex results in the generation of intracellular second messengers, IP3 and DG, which are derived from PI metabolism. The second messengers lead to increases in [Ca2+]i and activation of pkC, events causally linked to various cellular responses, including the production of IL-2 through as yet poorly defined pathways. Little is known about how other cell surface molecules that may provide an accessory function participate in such events. However, future genetic and biochemical studies are likely to shed light upon the mechanisms of signal transduction by the CD3/Ti complex and accessory molecules and the details of the intracellular events involved in the activation of a host of cellular genes associated with activation.

The endogenous constituents of human neutrophils that enhance the adherence of the neutrophils to surfaces have been isolated from sonicates of purified neutrophils. The predominant adherence-enhancing activity in the neutrophil sonicates cofiltered on Sephadex G-75 with a major peak of chemotactic inhibitory activity and exhibited approximately 30,000 mol wt. Sequential isoelectric focusing and electrophoresis in glycerol gradients of the 30,000-mol wt activities resolved two distinct acidic protein with isoelectric points of 3.6-3.8 and 3.3-3.4 that were designated the neutrophil adherence factor (NAF) I and II, respectively. Glutamic acid and aspartic acid together accounted for a total of 18 and 19% of the amino acids in purified preparations of NAF I and NAF II, respectively, whereas the basic amino acids lysine, arginine, and histidine represented <2 and 3% of the total residues. The preincubation of portions of 2 x 10(6) neutrophils with as little as 6 pmol of NAF I or 9 pmol of NAF II enhanced adherence to plastic petri dishes and inhibited chemotactic migration to a maximal extent, with comparable dose-response relationships for the two effects. Neither of the NAF was cytotoxic, exhibited substantial neutrophil chemotactic or chemokinetic activity, or influenced the phagocytosis of sheep erythrocytes sensitized with immunoglobulin (Ig)G. Analyses of subcellular fractions of neutrophils indicated that the NAF are contained predominantly in the specific granules. These distinctive acidic proteins of the specific granules of human neutrophils represent a new class of endogenous constituents that may regulate the involvement of neutrophils in inflammation.