Murine extramedullary erythropoiesis induced by tick infestation

The Innate Immune Response to Infection Induces Erythropoietin-Dependent Replenishment of the Dendritic Cell Compartment

Dendritic cells (DC) play a key role in the adaptive immune response due to their ability to present antigens and stimulate naïve T cells. Many bacteria and viruses can efficiently target DC, resulting in impairment of their immunostimulatory function or elimination. Hence, the DC compartment requires replenishment following infection to ensure continued operational readiness of the adaptive immune system. Here, we investigated the molecular and cellular mechanisms of inflammation-induced DC generation. We found that infection with viral and bacterial pathogens as well as Toll-like receptor 9 (TLR9) ligation with CpG-oligodeoxynucleotide (CpG-ODN) expanded an erythropoietin (EPO)-dependent TER119⁺CD11a⁺ cell population in the spleen that had the capacity to differentiate into TER119⁺CD11c^high and TER119^-CD11c^high cells both in vitro and in vivo. TER119⁺CD11c^high cells contributed to the conventional DC pool in the spleen and specifically increased in lymph nodes draining the site of local inflammation. Our results reveal a so far undescribed inflammatory EPO-dependent pathway of DC differentiation and establish a mechanistic link between innate immune recognition of potential immunosuppressive pathogens and the maintenance of the DC pool during and after infection.

Histological Disorganization of Spleen Compartments and Severe Visceral Leishmaniasis

The spleen is a secondary lymphoid organ responsible for immune surveillance against blood-circulating pathogens. Absence of the spleen is associated with increased susceptibility to systemic spread and fatal infection by different pathogens. Severe forms of visceral leishmaniasis are associated with disorganization of spleen compartments where cell interactions essential for splenic immunological function take place. White pulp atrophies, secondary lymphoid follicles and marginal zones vanish, and the boundaries separating white and red pulp blur. Leukocyte populations are reduced or disappear or are replaced by plasma cells. In this paper, we review the published data on spleen disorganization in severe forms of visceral leishmaniasis and propose a histological classification to help the exchange of information among research groups.

Gene expression of the liver of vaccination-protected mice in response to early patent infections of Plasmodium chabaudi blood-stage malaria

BACKGROUND

The role of the liver for survival of blood-stage malaria is only poorly understood. In experimental blood-stage malaria with Plasmodium chabaudi, protective vaccination induces healing and, thus, survival of otherwise lethal infections. This model is appropriate to study the role of the liver in vaccination-induced survival of blood-stage malaria.

METHODS

Female Balb/c mice were vaccinated with a non-infectious vaccine consisting of plasma membranes isolated in the form of erythrocyte ghosts from P. chabaudi-infected erythrocytes at week 3 and week 1 before infection with P. chabaudi blood-stage malaria. Gene expression microarrays and quantitative real-time PCR were used to investigate the response of the liver, in terms of expression of mRNA and long intergenic non-coding (linc)RNA, to vaccination-induced healing infections and lethal P. chabaudi malaria at early patency on day 4 post infection, when parasitized erythrocytes begin to appear in peripheral blood.

RESULTS

In vaccination-induced healing infections, 23 genes were identified to be induced in the liver by > tenfold at p < 0.01. More than one-third were genes known to be involved in erythropoiesis, such as Kel, Rhag, Ahsp, Ermap, Slc4a1, Cldn13 Gata1, and Gfi1b. Another group of > tenfold expressed genes include genes involved in natural cytotoxicity, such as those encoding killer cell lectin-like receptors Klrb1a, Klrc3, Klrd1, the natural cytotoxicity-triggering receptor 1 Ncr1, as well as the granzyme B encoding Gzmb. Additionally, a series of genes involved in the control of cell cycle and mitosis were identified: Ccnb1, Cdc25c, Ckap2l were expressed > tenfold only in vaccination-protected mice, and the expression of 22 genes was at least 100% higher in vaccination-protected mice than in non-vaccinated mice. Furthermore, distinct lincRNA species were changed by > threefold in livers of vaccination-protected mice, whereas lethal malaria induced different lincRNAs.

CONCLUSION

The present data suggest that protective vaccination accelerates the malaria-induced occurrence of extramedullary erythropoiesis, generation of liver-resident cytotoxic cells, and regeneration from malaria-induced injury in the liver at early patency, which may be critical for final survival of otherwise lethal blood-stage malaria of P. chabaudi.

Virulence of recurrent infestations with Borrelia-infected ticks in a Borrelia-amplifying bird

Lyme disease cases caused by Borrelia burgdorferi s.l. bacteria is increasing steadily in Europe, in part due to the expansion of the vector, Ixodes ricinus. Wild reservoir hosts are typically recurrently infested. Understanding the impact of these cumulative parasite exposures on the host's health is, therefore, central to predict the distribution of tick populations and their pathogens. Here, we have experimentally investigated the symptoms of disease caused by recurrent infestations in a common songbird (Parus major). Birds were exposed three times in succession to ticks collected in a Borrelia endemic area. Health and immune measures were analyzed in order to investigate changes in response to tick infestation and Borrelia infection rate. Nitric oxide levels increased with the Borrelia infection rate, but this effect was increasingly counteracted by mounting tick infestation rates. Tick infestations equally reduced haematocrit during each cycle. But birds overcompensated in their response to tick feeding, having higher haematocrit values during tick-free periods depending on the number of ticks they had been previously exposed to. Body condition showed a similar overshooting response in function of the severity of the Borrelia infection. The observed overcompensation increases the bird's energetic needs, which may result in an increase in transmission events.

Transcriptional profiling of the murine cutaneous response during initial and subsequent infestations with Ixodes scapularis nymphs

BACKGROUND

Ixodes scapularis ticks are hematophagous arthropods capable of transmitting many infectious agents to humans. The process of blood feeding is an extended and continuous interplay between tick and host responses. While this process has been studied extensively in vitro, no global understanding of the host response to ticks has emerged.

METHODS

To address this issue, we used PCR-arrays to measure skin-specific expression of 233 discrete genes at 8 time points during primary and secondary infestations of mice with pathogen-free I. scapularis nymphs. Selected results were then validated at the mRNA and protein levels by additional real-time PCR and bioplex assay.

RESULTS

Primary infestation was characterized by the late induction of an innate immune response. Lectin pattern recognition receptors, cytokines, and chemokines were upregulated consistent with increased neutrophil and macrophage migration. Gene ontology and pathway analyses of downregulated genes suggested inhibition of gene transcription and Th17 immunity. During the secondary infestation, additional genes were modulated suggesting a broader involvement of immune cells including CD8 and CD4 positive T lymphocytes. The cytokine response showed a mixed Th1/Th2 profile with a potential for T regulatory cell activity. Key gene ontology clusters observed during the secondary infestation were cell migration and activation. Matrix metalloproteinases were upregulated, apoptosis-related genes were differentially modulated, and immunoreceptor signaling molecules were upregulated. In contrast, transcripts related to mitogenic, WNT, Hedgehog, and stress pathways were downregulated.

CONCLUSIONS

Our results support a model of tick feeding where lectin pattern recognition receptors orchestrate an innate inflammatory response during primary infestation that primes a mixed Th1/Th2 response upon secondary exposure. Tick feeding inhibits gene transcription and Th17 immunity. Salivary molecules may also inhibit upregulation of mitogenic, WNT, Hedgehog, and stress pathways and enhance the activity of T regulatory cells, production of IL-10, and suppressors of cytokine signaling molecules (SOCS). This study provides the first comprehensive transcriptional analysis of the murine host response at the I. scapularis bite site and suggests both a potential model of the host cutaneous response and candidate genes for further description and investigation.

Modulation of cutaneous inflammation induced by ticks in contrasting phenotypes of infestation in bovines

Tick saliva contains molecules that are inoculated at the site of attachment on their hosts in order to modulate local immune responses and facilitate a successful blood meal. Bovines express heritable, contrasting phenotypes of infestations with the cattle tick, Rhipicephalus (Boophilus) microplus: breeds of Bos taurus indicus are significantly more resistant than those of Bos taurus taurus. Tick saliva may contain molecules that interfere with adhesion of leukocytes to endothelium and resistant hosts may mount an inflammatory profile that is more efficient to hamper the tick's blood meal. We show in vitro that adhesion of peripheral blood mononuclear cells to monolayers of cytokine-activated bovine umbilical endothelial cells was significantly inhibited by tick saliva. The inflammatory response to bites of adults of R. microplus mounted by genetically resistant and susceptible bovine hosts managed in the same pasture was investigated in vivo. The inflammatory infiltrates and levels of message coding for adhesion molecules were measured in biopsies of tick-bitten and control skin taken when animals of both breeds were exposed to low and high tick infestations. Histological studies reveal that cutaneous reactions of resistant hosts to bites of adult ticks contained significantly more basophils and eosinophils compared with reactions of the susceptible breed. Expression of the adhesion molecules - intercellular adhesion molecule-1 (ICAM-1), vascular cell adhesion molecule 1 (VCAM-1) and P-selectin - was higher in adult-infested skin of susceptible hosts undergoing low infestations compared to resistant hosts; when host was exposed to high infestations expression of these adhesion molecules was down-regulated in both phenotypes of infestations. Expression of leukocyte adhesion glycoprotein-1 (LFA-1) was higher in skin from susceptible hosts undergoing low or high infestations compared to resistant hosts. Conversely, higher levels of E-selectin, which promotes adhesion of memory T cells, were expressed in skin of resistant animals. This finding may explain the resistant host's ability to mount more rapid and efficient secondary responses that limit hematophagy and infestations. The expression profiles observed for adhesion molecules indicate that there are differences in the kinetics of the inflammatory reactions mounted by resistant and susceptible hosts and the balance between tick and host is affected by the number of tick bites a host receives. We show that the contrasting phenotypes of infestations seen in bovines infested with R. microplus are correlated with differences in the cellular and molecular composition of inflammatory infiltrates elicited by bites with adult ticks.

Influence of the Ixodes ricinus tick blood-feeding on the antigen-specific antibody response in vivo

The blood meal of hard ticks such as Ixodes ricinus lasts several days. This is made possible by tick salivary factors that inhibit inflammation, haemostasis and the host immune response. We assessed the latter on a model of immune response in vivo. A significant reduction of specific IgM and IgG levels was observed in BALB/c mice infested 5 days before injection with bovine serum albumin (BSA) and QuilA but not in mice infested 5 days after the immunization. This effect was not observed in mock-infested mice and could not be attributed to the use of anesthetics. The antibody response was not merely delayed and the Th(1)/Th(2) balance appeared not altered. T-dependent zones and germinal centers in lymph nodes draining the tick bite site showed no apparent morphological alterations or shift in T cell subpopulations. However, the spleens of tick-infested mice had also an enlarged red pulp, indicating an increased extramedullary haematopoietic activity.