Beth A. Garvy

Cyclic ADP-ribose production by CD38 regulates intracellular calcium release, extracellular calcium influx and chemotaxis in neutrophils and is required for bacterial clearance in vivo.

Cyclic ADP-ribose is believed to be an important calcium-mobilizing second messenger in invertebrate, mammalian and plant cells. CD38, the best-characterized mammalian ADP-ribosyl cyclase, is postulated to be an important source of cyclic ADP-ribose in vivo. Using CD38-deficient mice, we demonstrate that the loss of CD38 renders mice susceptible to bacterial infections due to an inability of CD38-deficient neutrophils to directionally migrate to the site of infection. Furthermore, we show that cyclic ADP-ribose can directly induce intracellular Ca++ release in neutrophils and is required for sustained extracellular Ca++ influx in neutrophils that have been stimulated by the bacterial chemoattractant, formyl-methionyl-leucyl-phenylalanine (fMLP). Finally, we demonstrate that neutrophil chemotaxis to fMLP is dependent on Ca++ mobilization mediated by cyclic ADP-ribose. Thus, CD38 controls neutrophil chemotaxis to bacterial chemoattractants through its production of cyclic ADP-ribose, and acts as a critical regulator of inflammation and innate immune responses.

B Cells Are Required for Generation of Protective Effector and Memory CD4 Cells in Response to Pneumocystis Lung Infection

B cell-deficient mice are susceptible to infection by Pneumocystis carinii f. sp. muris (PC). To determine whether this susceptibility is due to a requirement for B cells to prime T cells, we compared CD4 T cell responses to PC in bone marrow chimeric mice that express MHC class II (MHCII) on all APCs (wild-type (WT) chimeras) and in bone marrow chimeric mice that express MHCII on all APCs except B cells (MHCII−/− chimeras). Although PC was rapidly cleared by WT chimeric mice, PC levels remained high in chimeric mice that lacked MHCII on B cells. In addition, although T cells were primed in the draining lymph nodes of MHCII−/− chimeric mice, the number of activated CD4 T cells infiltrating the lungs of these mice was reduced relative to the number in the lungs of WT chimeras. We also adoptively transferred purified CD4 T cells from the draining lymph nodes of PC-infected normal or B cell-deficient mice into SCID mice. Mice that received CD4 cells from normal mice were able to mount a response to infection in the lungs and clear PC. However, mice that received CD4 cells from B cell-deficient mice had a delayed T cell response in the lungs and failed to control the infection. These data indicate that B cells play a vital role in generation of CD4+ memory T cells in response to PC infection in the lungs.

Clearance of Pneumocystis carinii in Mice Is Dependent on B Cells But Not on P. carinii-Specific Antibody

Both CD4+ T cells and B cells are critical for defense against Pneumocystis carinii infection; however, the mechanism by which B cells mediate protection is unknown. We show that P. carinii-specific IgM is not sufficient to mediate clearance of P. carinii from the lungs since CD40-deficient mice produced normal levels of specific IgM, but were unable to clear the organisms. Using chimeric mice in which the B cells were deficient in CD40 (CD40KO chimeras) we found that clearance of P. carinii infection is delayed compared with wild-type controls. These CD40KO chimeric mice produced normal levels of P. carinii-specific IgM, but did not produce class-switched IgG or IgA. Similarly, clearance of P. carinii was delayed in mice deficient in FcγRI and III (FcγRKO), indicating that P. carinii-specific IgG partially mediates opsonization and clearance of P. carinii. Opsonization of organisms by complement did not compensate for the lack of specific IgG or FcγR, since C3-deficient and C3-depleted FcγRKO mice were still able to clear P. carinii. Finally, μMT and CD40KO chimeric mice had reduced numbers of activated CD4+ T cells in the lungs and lymph nodes compared with wild-type mice, suggesting that B cells are important for activation of T cells in response to P. carinii. Together these data indicate that P. carinii-specific IgG plays an important, but not critical, role in defense against P. carinii. Moreover, these data suggest that B cells also mediate host defense against P. carinii by facilitating CD4+ T cell activation or expansion.

The importance of neutrophils in resistance to pneumococcal pneumonia in adult and neonatal mice

Neonatal mice succumbed to intranasally-inoculatedStreptococcus pneumoniae doses which were as much as 250 times less than the doses that adult mice were resistant to. Neutrophil migration into lungs of neonates was similar in kinetics and intensity to that in adults in response to lethal doses ofS. pneumoniae. Interestingly, neutrophil infiltration into the lung alveoli of neonates occured at lower doses of bacteria than that required for similar responses in adults. Furthermore, depletion of neutrophils in adult and neonatal mice inoculated with low doses of bacteria resulted in significantly higher lung burdens of bacteria in neonatal mice as compared to adults. These data indicate that increased susceptibility of neonates toS. pneumoniae is not the result of incompletely developed neutrophil function and infact, indicate that neutrophils contribute more to resistance to low doses ofS. pneumoniae in neonates than they do in adult mice.

IL-10 Modulates Host Responses and Lung Damage Induced by Pneumocystis carinii Infection

Host responses to Pneumocystis carinii infection mediate impairment of pulmonary function and contribute to the pathogenesis of pneumonia. IL-10 is known to inhibit inflammation and reduce the severity of pathology caused by a number of infectious organisms. In the present studies, IL-10-deficient (IL-10 knockout (KO)) mice were infected with P. carinii to determine whether the severity of pathogenesis and the efficiency of clearance of the organisms could be altered in the absence of IL-10. The clearance kinetics of P. carinii from IL-10 KO mice was significantly enhanced compared with that of wild-type (WT) mice. This corresponded to a more intense CD4+ and CD8+ T cell response as well as an earlier neutrophil response in the lungs of IL-10 KO mice. Furthermore, IL-12, IL-18, and IFN-γ were found in the bronchoalveolar lavage fluids at earlier time points in IL-10 KO mice suggesting that alveolar macrophages were activated earlier than in WT mice. However, when CD4+ cells were depleted from P. carinii-infected IL-10 KO mice, the ability to enhance clearance was lost. Furthermore, CD4-depleted IL-10 KO mice had significantly more lung injury than CD4-depleted WT mice even though the intensity of the inflammatory responses was similar. This was characterized by increased vascular leakage, decreased oxygenation, and decreased arterial pH. These data indicate that IL-10 down-regulates the immune response to P. carinii in WT mice; however, in the absence of CD4+ T cells, IL-10 plays a critical role in controlling lung damage independent of modulating the inflammatory response.

Azithromycin Alters Macrophage Phenotype and Pulmonary Compartmentalization during Lung Infection with Pseudomonas

ABSTRACT Infection with mucoid strains of Pseudomonas aeruginosa in chronic inflammatory diseases of the airway is difficult to eradicate and can cause excessive inflammation. The roles of alternatively activated and regulatory subsets of macrophages in this pathophysiological process are not well characterized. We previously demonstrated that azithromycin induces an alternatively activated macrophage-like phenotype in vitro. In the present study, we tested whether azithromycin affects the macrophage activation status and migration in the lungs of P. aeruginosa-infected mice. C57BL/6 mice received daily doses of oral azithromycin and were infected intratracheally with a mucoid strain of P. aeruginosa. The properties of macrophage activation, immune cell infiltration, and markers of pulmonary inflammation in the lung interstitial and alveolar compartments were evaluated postinfection. Markers of alternative macrophage activation were induced by azithromycin treatment, including the surface expression of the mannose receptor, the upregulation of arginase 1, and a decrease in the production of proinflammatory cytokines. Additionally, azithromycin increased the number of CD11b+ monocytes and CD4+ T cells that infiltrated the alveolar compartment. A predominant subset of CD11b+ cells was Gr-1 positive (Gr-1+), indicative of a subset of cells that has been shown to be immunoregulatory. These differences corresponded to decreases in neutrophil influx into the lung parenchyma and alteration of the characteristics of peribronchiolar inflammation without any change in the clearance of the organism. These results suggest that the immunomodulatory effects of azithromycin are associated with the induction of alternative and regulatory macrophage activation characteristics and alteration of cellular compartmentalization during infection.

Neonatal T Cells in an Adult Lung Environment Are Competent to Resolve Pneumocystis carinii Pneumonia

Initiation of the pulmonary inflammatory response to Pneumocystis carinii is delayed by 3 wk in mice infected as neonates compared with adults. There was no difference in the proliferative response of draining lymph node T cells from mice infected as neonates compared with adults when stimulated in vitro with either Con A or anti-CD3 mAb. However, TNF-α and IFN-γ mRNA expression in the lungs of P. carinii-infected neonates was significantly lower than in adults indicating a lack of appropriate activation signaling in the local environment. This may have been due to active suppression because TGF-β mRNA expression was significantly elevated in neonatal lungs compared with adults. To determine whether T cells from 10-day-old mice would effect resolution of P. carinii if harbored in an adult lung environment, cells were adoptively transferred to SCID mice with established P. carinii infections. There was no difference in the kinetics of T cell migration into the lungs or of clearance of P. carinii organisms when SCID mice were reconstituted with splenocytes from young mice as compared with adult mice. Furthermore, splenocytes from young mice stimulated both TNF-α and IFN-γ mRNA expression to levels that were similar to that in the lungs of SCID mice reconstituted with adult cells. These data indicate that neonatal lymphocytes are competent to resolve P. carinii infection when harbored in an adult lung environment, suggesting that the neonatal lung environment, and not the T cells, is ineffective at responding to P. carinii infection.

Delayed Inflammatory Response to Pneumocystis carinii Infection in Neonatal Mice Is Due to an Inadequate Lung Environment

Challenge of neonatal mice with an intranasal inoculation of Pneumocystis carinii results in a subclinical infection that takes 6 wk to resolve, whereas adult mice resolve a comparable challenge within 3 wk. This delayed clearance is due to a delayed inflammatory response in neonatal mice; however, the reason for this delay has been unknown. To determine whether the neonatal lung environment is sufficient to attract immunocompetent lymphocytes into the lungs, an adoptive transfer strategy was employed in which splenocytes from adult BALB/c mice were transferred into P. carinii-infected neonatal or adult SCID mice. All adults, but no pups, resolved their infections by day 37 postreconstitution. Despite reconstitution with adult splenocytes, pups had a negligible lung inflammatory response until day 24, whereas adult mice had activated CD4+ and CD8+ cells in the lung by day 13. The delay in neonates corresponded to delayed kinetics of expression of lung cytokines TNF-α and IFN-γ mRNA and chemokines lymphotactin, RANTES, and macrophage inflammatory protein-1β mRNA. Phagocytic cells from neonatal mice were significantly less efficient than adult cells at migrating to the draining lymph nodes after phagocytosing fluorescent beads. There were fewer dendritic cells and Ia+ myeloid cells in the lungs of P. carinii-infected neonatal mice compared with adults. These data indicate that the lung environment of neonatal mice is insufficient for migration of T cells, due at least in part to inefficient phagocytosis and migration of APCs to the lymph nodes as well as delayed chemokine and TNF-α mRNA expression.

TNF-α-Dependent ICAM-1- and VCAM-1-Mediated Inflammatory Responses Are Delayed in Neonatal Mice Infected with Pneumocystis carinii

Neonatal mice have a delayed CD4-mediated inflammatory response to Pneumocystis carinii (PC) infection in the lungs that corresponds to a delayed TNF-α response and a delayed clearance of the organisms compared with adult mice. Since TNF-α is known to drive the up-regulation of adhesion molecules, we examined the expression and function of adhesion molecules in the lungs of neonatal mice. The expression of both ICAM-1 and VCAM-1 was significantly lower in the lungs of PC-infected neonatal mice compared with adults. Additionally, migration of neonatal T cells across endothelial cells expressing VCAM-1 and monocyte chemotactic protein-1 was aberrant compared with that in adult T cells, although α4β1 integrin-mediated adhesion of neonatal lymphocytes was comparable to that of adult lymphocytes. Treatment of neonatal mice with exogenous TNF-α resulted in increased expression of ICAM-1 and VCAM-1 as well as increased expression of chemokines, resulting in infiltration of CD4+ cells into the lungs. Treatment with exogenous TNF-α resulted in a trend (although not statistically significant) toward a reduction of PC organisms from the lungs. These data indicate that neonatal lung endothelial cells do not up-regulate ICAM-1 and VCAM-1 in response to PC infection, probably due to depressed TNF-α production. Additionally, neonatal T cells are defective in the ability to migrate across endothelial cells.

Scavenger receptor A dampens induction of inflammation in response to the fungal pathogen Pneumocystis carinii

ABSTRACT Alveolar macrophages are the effector cells largely responsible for clearance of Pneumocystis carinii from the lungs. Binding of organisms to β-glucan and mannose receptors has been shown to stimulate phagocytosis of the organisms. To further define the mechanisms used by alveolar macrophages for clearance of P. carinii, mice deficient in the expression of scavenger receptor A (SRA) were infected with P. carinii, and clearance of organisms was monitored over time. SRA-deficient (SRAKO) mice consistently cleared P. carinii faster than did wild-type control mice. Expedited clearance corresponded to elevated numbers of activated CD4+ T cells in the alveolar spaces of SRAKO mice compared to wild-type mice. Alveolar macrophages from SRAKO mice had increased expression of CD11b on their surfaces, consistent with an activated phenotype. However, they were not more phagocytic than macrophages expressing SRA, as measured by an in vivo phagocytosis assay. SRAKO alveolar macrophages produced significantly more tumor necrosis factor alpha (TNF-α) than wild-type macrophages when stimulated with lipopolysaccharide in vitro but less TNF-α in response to P. carinii in vitro. However, upon in vivo stimulation, SRAKO mice produced significantly more TNF-α, interleukin 12 (IL-12), and IL-18 in response to P. carinii infection than did wild-type mice. Together, these data indicate that SRA controls inflammatory cytokines produced by alveolar macrophages in the context of P. carinii infection.