Polymorphonuclear Neutrophils Improve Replication ofChlamydia pneumoniaeIn Vivo upon MyD88-Dependent Attraction

Abstract

Chlamydia pneumoniae, an obligate intracellular bacterium, causes pneumonia in humans and mice. In this study, we show that GR1+/CD45+ polymorphonuclear neutrophils (PMN) surprisingly increase the bacterial load of C. pneumoniae in vivo. Upon intranasal infection of wild-type mice, the lung weight is increased; the cytokines TNF, IL-12p40, and IFN-γ, as well as the chemokines keratinocyte-derived chemokine, MCP-1, and MIP-2 are secreted; and GR1+/CD45+ PMN are recruited into lungs 3 days postinfection. In contrast, in infected MyD88-deficient mice, which lack a key adaptor molecule in the signaling cascade of TLRs and IL-1R family members, the increase of the lung weight is attenuated, and from the analyzed cyto- and chemokines, only IL-12p40 is detectable. Upon infection, almost no influx of inflammatory cells into lungs of MyD88-deficient mice can be observed. Six days postinfection, however, MyD88-deficient mice were able to produce TNF, IFN-γ, keratinocyte-derived chemokine, and MCP-1 in amounts similar to wild-type mice, but failed to secrete IL-12p40 and MIP-2. At this time point, the infection increased the lung weight to a level similar to wild-type mice. Curiously, the chlamydial burden in MyD88-deficient mice 3 days postinfection is lower than in wild-type mice, a finding that can be reproduced in wild-type mice by depletion of GR1+ cells. In analyzing how PMN influence the chlamydial burden in vivo, we find that PMN are infected and enhance the replication of C. pneumoniae in epithelial cells. Thus, the lower chlamydial burden in MyD88-deficient mice can be explained by the failure to recruit PMN.

Differential involvement of TLR2 and TLR4 in host survival during pulmonary infection with Chlamydia pneumoniae

“…However, in lungs of TLR2 -/-and TLR2 -/-ÂTLR4 d/d mice the number of C. pneumoniae IFU was lower than in WT or TLR4 d/d mice 3 days post infection (Fig. 4A), a finding which was similar to MyD88 -/-mice [19]. Comparison of chlamydial burden and pulmonary influx of PMN in TLR2 -/-, TLR2 -/-ÂTLR4 d/d , MyD88 -/-and WT mice at day 3 post infection revealed that the two parameters correlated with each other (Fig.…”

“…In contrast WT mice showed irregularly distributed foci of acute bronchopneumonia with intra-alveolar or intrabronchial aggregates of granulocytes and intense perivascular infiltrates at this point in time, a finding we already observed in MyD88 -/-mice (Fig. 7B) [19]. At 9 days post infection, TLR2 -/-ÂTLR4 d/d mice displayed widespread, acute parenchymal inflammation with epithelial cell necrosis, edema and massive intraalveolar infiltrates of granulocytes and mainly macrophages and lymphocytes, while WT mice still showed significant inflammatory infiltrates, but in addition accumulation of foam cells indicative of resorptive changes (Fig.…”

“…*p 0.008, recruited to the infected lung. Analysis of the pulmonary infiltrate by flow cytometry revealed that the percentage of PMN as defined by GR1 + /CD45 + expression [19] was increased in TLR2 -/-or TLR2 -/-ÂTLR4 d/d mice 3 days post infection compared to non-infected mice ( Fig. 2A, B).…”

Monocyte and neutrophil recruitment during oral Salmonella infection is driven by MyD88‐derived chemokines

“…Moreover, although chemokine-deficient models have shown increased bacterial burden during Salmonella infection, [19][20][21], it is not known which chemokines are induced in the intestinal lymphoid tissue during oral Salmonella infection or where and by what cells the chemokines are produced. Finally, although impaired recruitment of inflammatory cells in mice deficient in TLR pathways has been observed in some infection models [22,23], the role of the different TLR and the adaptor MyD88 in cell recruitment during oral Salmonella infection is not known.…”

“…Moreover, although chemokine-deficient models have shown increased bacterial burden during Salmonella infection, [19][20][21], it is not known which chemokines are induced in the intestinal lymphoid tissue during oral Salmonella infection or where and by what cells the chemokines are produced. Finally, although impaired recruitment of inflammatory cells in mice deficient in TLR pathways has been observed in some infection models [22,23], the role of the different TLR and the adaptor MyD88 in cell recruitment during oral Salmonella infection is not known.Thus, the aims of this study were to use an oral Salmonella infection model to: (i) investigate chemokine induction and the cellular sources in the PP and MLN when phagocyte influx is first observed; (ii) localize chemokine production in infected PP using laser capture microdissection microscopy; (iii) assess distribution of phagocytes recruited to infected PP by fluorescence microscopy and (iv) establish the relationship between TLR, chemokine production and phagocyte recruitment. The data provide insight into the chemokine milieu that orchestrates the early recruitment of phagocytes to combat oral Salmonella infection.…”