Role of Toll-Like Receptor 4 in Induction of Cell-Mediated Immunity and Resistance toBrucella abortusInfection in Mice

Abstract

Initial host defense to bacterial infection is executed by innate immunity, and therefore the main goal of this study was to examine the contribution of Toll-like receptors (TLRs) during Brucella abortus infection. CHO reporter cell lines transfected with CD14 and TLRs showed that B. abortus triggers both TLR2 and TLR4. In contrast, lipopolysaccharide (LPS) and lipid A derived from Brucella rough (R) and smooth (S) strains activate CHO cells only through TLR4. Consistently, macrophages from C3H/HePas mice exposed to R and S strains and their LPS produced higher levels of tumor necrosis factor alpha (TNF-␣) and interleukin-12 compared to C3H/HeJ, a TLR4 mutant mouse. The essential role of TLR4 for induction of proinflammatory cytokines was confirmed with diphosphoryl lipid A from Rhodobacter sphaeroides. Furthermore, to determine the contribution of TLR2 and TLR4 in bacterial clearance, numbers of Brucella were monitored in the spleen of C3H/HeJ, C3H/HePas, TLR2 knockout, and wild-type mice at 1, 3, and 6 weeks following B. abortus infection. Interestingly, murine brucellosis was markedly exacerbated at weeks 3 and 6 after infection in animals that lacked functional TLR4 (C3H/HeJ) compared to C3H/HePas that paralleled the reduced gamma interferon production by this mouse strain. Finally, by mass spectrometry analysis we found dramatic differences on the lipid A profiles of R and S strains. In fact, S lipid A was shown to be more active to trigger TLR4 than R lipid A in CHO cells and more effective in inducing dendritic cell maturation. In conclusion, these results indicate that TLR4 plays a role in resistance to B. abortus infection and that S lipid A has potent adjuvant activity.

TLR2 and TLR4 signaling pathways are required for recombinant Brucella abortus BCSP31-induced cytokine production, functional upregulation of mouse macrophages, and the Th1 immune response in vivo and in vitro

“…60,87 TLR4 mutant mice are more susceptible to infection with B. abortus S2308 strain than normal mice. 88 Moreover, the replication of B. abortus S19 strain and S2308 strain in vivo has also been demonstrated to be TLR4-independent. 89 Interestingly, Pei et al 90 have demonstrated that TLR4 is involved in the internalization of smooth B. abortus in macrophages.…”

Pathogenesis and Immunobiology of Brucellosis

“…These reductionist approaches led to the conclusion that Brucella persists in nutrient-poor BCVs within the host, 35 in which the organism replicates and from which infection spreads with minimal activation of the host cell. 36 In contrast to the numerous metabolic functions shown to be necessary for intracellular replication, the T4SS stood out as a notable target for further investigation of virulence potential. 37,38 Yet despite a decade of research, the complete mechanism of action remains undefined.…”

NFB is differentially activated in macrophages from J774A.1 cell line infected with vaccine or virulent strains of Brucella abortus

“…Most papers analyze the late response, in which there is also an association between the presence of IL-12 and IFN- and protection. The second stage of production of these cytokines completes a response model in which both cytokines form a positive feedback loop (Campos et al, 2004;Huang et al, 2003;Paranavitana et al, 2005).…”

“…These findings are related with our work, since B. abortus 2308 replicated much faster within the macrophage than the RB51 strain (data not shown); hence, bacterial growth could inhibited in some way TNF-α and IL-6 production. On the other hand, LPS starts a complex cascade of events, particularly in monocytes and macrophages that lead to the production of proinflammatory cytokines (Campos et al, 2004;Harju et al, 2001). Binding of LPS to TLR2 and TLR4, in conjunction with MD2, starts the cytoplasmic signaling cascade that leads to IB degradation, nuclear translocation of NF-B, and transcriptional activation of the genes of the proinflammatory response Liew et al, 2005), such as the cytokines IL-1, IL-6, IL-12, TNF-α, adhesion molecules, acute stage proteins, and inducible enzymes, such as iNOS and COX-2 (Liew et al, 2005;Zhang and Ghosh, 2001).…”

“…Complex II could be responsible for the lack of gene expression of the analyzed cytokines since it is well documented that the homodimer p50-p50 of NF-B is not a transcriptional activator (El Gazzar et al, 2007;Pereira et al, 2005;Plaksin et al, 1993). Brucella, with its nonclassical LPS, leads to a decreased production of cytokines by monocytes and macrophages, including TNF-α, IL-1 and IL-6 (Campos et al, 2004;Jimenez de Bagues et al, 2005;, and iNOS (López-Urrutia et al, 2000;Wang et al, 2001). In our hands, characterization of NF-B proteins revealed a predominance of p50-p50 homodimer in 2308-infected macrophages.…”