Kinetics of CD11b/CD18 Up-Regulation During Infection with the Agent of Human Granulocytic Ehrlichiosis in Mice

Abstract

SUMMARY:The agent of human granulocytic ehrlichiosis (aoHGE) is a tick-borne, obligate intracellular, granulocytotropic bacterium able to infect numerous host species. Given its unique niche and the leukopenia often noted with infection, we investigated the effect of acute aoHGE infection on neutrophil activation by evaluating surface expression of the ␤2 integrin CD11b/CD18 in a mouse model using FACS analysis. Infection resulted in neutrophil activation with up-regulation of CD11b/CD18 in multiple strains of mice, however, hematologic analysis showed no apparent role for CD11b/CD18 in mediating peripheral leukopenia. Because IFN-␥ is an important cytokine during granulocytic ehrlichiosis and is known to activate leukocytes, we investigated the potential role of IFN-␥ in CD11b/CD18 up-regulation. Neutrophils from IFN-␥ knock-out mice became activated during aoHGE infection, however, the kinetics of activation differed from wild-type mice. In addition, activation correlated directly with the presence of bacteria because neutrophils with large intracytoplasmic morula also expressed higher levels of CD11b/CD18. CD11b/CD18 seemed to be critical to early bacterial clearance and killing in vivo because infection of mice with targeted genetic disruption of CD11b/CD18 resulted in an initial increase in bacterial burden compared with wild-type mice. Similarly, in vitro culture of neutrophils from infected CD11b/CD18 knock-out mice resulted in a marked increase in bacterial proliferation compared with congenic controls. The data support crucial roles of CD11b/CD18 and IFN-␥-mediated cell activation as mechanisms that limit bacterial replication. (Lab Invest 2002, 82:303-311).

Infection withAnaplasma phagocytophilumInduces Multilineage Alterations in Hematopoietic Progenitor Cells and Peripheral Blood Cells

“…Infection of C3H mice was performed either by infestation with infected nymphal ticks (11) or by intraperitoneal (i.p.) injection of infected SCID mouse blood (10,33), exactly as previously described. Both routes of inoculation result in successful infection with similar kinetics (32); however, tick infestation is more complicated and time-consuming.…”

“…Hematologic data for mice infected via i.p. injection have been published previously (10,12,33 5 unfractionated BM cells from each mouse using a Qiagen DNeasy tissue kit (Qiagen, Valencia, CA) according to manufacturer's instructions and exactly as previously described (10,11). DNA amplification to determine the A. phagocytophilum p44 copy number, data acquisition, and data analysis were performed with an ABI Prism 7700 sequence detector (Perkin-Elmer, Applied Biosystems, Foster City, CA) exactly as previously described (10,32).…”

“…GA is an emerging, tick-borne infectious disease (26). Unlike endotoxin-mediated events, infection with A. phagocytophilum typically results in multiple cytopenias in natural disease in both humans (5) and animals (7,43,48), as well as in animal models of infection (10,12,33). The cytopenias typically include mild nonregenerative anemia, mild to moderate leukopenia, and moderate to marked thrombocytopenia.…”

“…The mechanism(s) underlying the cytopenias are not fully understood. Immune-mediated destruction or splenic sequestration of cells is unlikely as cytopenias occur within the first 2 to 5 days of infection, before a significant acquired immune response is mounted, SCID mice (lacking functional B and T cells) become cytopenic (10,12,33), and splenectomized mice become thrombocytopenic (12).…”

Experimental Infection of C3H/HeJ Mice with the NY18 Isolate of Anaplasma phagocytophilum

“…While mice do not consistently develop signs of clinical disease as described in humans, horses, or nonhuman primates, they do develop an acute infection and associated pathologic changes. 1,[7][8][9][10]12,13,15,23,24,31,38,39,42,46 In this study we report the results of a pathologic study of acute A phagocytophilum infection in C3H/HeJ mice and discuss the relative importance and advantages of this mouse model in contrast to other A phagocytophilum models and hosts.…”