Publikationsserver der RWTH Aachen University
A Leishmania ortholog of macrophage migration inhibitory factor modulates host macrophage responses
Abstract
dc:descriptionParasitic organisms have evolved specialized strategies to evade host immune defense mechanisms. This thesis describes the characterization of two Leishmania major-encoded orthologs of the pro-inflammatory pleiotropic cytokine, macrophage migration inhibitory factor (MIF). These two MIF-like sequences show 22% sequence identity when aligned with human MIF, and are most likely the result of gene duplication. The Lm1740MIF and Lm1750MIF genes (58% identity) are expressed in all developmental stages of L. major. Interestingly, LmMIF expression levels were shown to be significantly up-regulated in the procyclic life-stage of the parasite, which exists solely in the host sand fly. Furthermore, Lm1750MIF levels were 3–4 fold higher than Lm1740MIF levels. The finding that LmMIF is expressed in procyclic parasites might reveal a new function for MIF within its vector, the sandfly. Furthermore, the work described here postulated that Lm1740MIF might interact with the macrophage surface receptor, CD74. To evaluate this hypothesis, binding analyses using surface plasmon resonance (Biacore) were carried out. The Kd of MIF was previously approximated to be between 9 × 10-9 to 2.3 × 10-10. Lm1740MIF showed a significant binding interaction with CD74 (Kd=2.9 × 10-8 M). Thus, there is sufficient structural homology between Lm1740MIF and human MIF to permit high-affinity binding to CD74. To investigate whether Lm1740MIF induces ERK1/2 activation in a CD74-dependent manner and to determine if it inhibits activation-induced macrophage apoptosis similar to its mammalian counterpart, the ability of Lm1740MIF to stimulate ERK1/2 phosphorylation as well as to inhibit Ser15 phosphorylation of the tumor suppressor p53 was tested. Macrophages treated with Lm1740MIF were assessed for apoptosis by the ELISA method; additionally, Western blot analyses for ERK1/2 and p53 activation were performed. The interaction between Lm1740MIF and CD74 led to an similar signal transduction response in macrophages obtained from both wild-type and C3H/HeJ mice, indicating that signaling was not due to the presence of contaminating endotoxin. Lm1740MIF was functionally active in both ERK1/2 signaling and protection from apoptosis, although the level of activity was generally lower than for mammalian MIF, an observation that appeared consistent with the lower Kd of Lm1740MIF for the CD74 receptor. For mouse MIF, protection from apoptosis was dependent on CD74, and the response was associated with a decrease in the cytoplasmic content of Ser15-phosphorylated p53. The ability of Lm1740MIF to inhibit apoptosis may facilitate the persistence of Leishmania within macrophages and contribute to its evasion from immune destruction. The precise cellular pathway by which Lm1740MIF activates CD74 and whether Lm1740MIF modulates additional pathways that are important for either intracellular parasitism or for immune evasion remains to be determined. In conclusion, the presented results indicate that a Leishmania ortholog of the cytokine MIF has the ability to activate the human MIF receptor and influence the functional responses of monocytes/macrophages. Because Leishmania is an intracellular infection of monocytes/macrophages, Leishmania-encoded MIF is hypothesized to sustain monocyte/macrophage survival and contribute to the persistence of the parasite for completion of its infectious life cycle. While these data are consistent with a role for Leishmania MIF in modulating host-immune responses, they do not exclude the possibility that Lm1740MIF may function in the growth and/or replication of the parasite.
Degree
thesis:*- Grantor dc:publisher
- Publikationsserver der RWTH Aachen University
- Year dc:date
- 2008
Author and committee
dc:creator, dc:contributor.*- Author dc:creator
-
- Kamir, Daniela
- Contributors dc:contributor
-
- Bernhagen, Jürgen
Subjects
dc:subject × 8Rights
dc:rights- Statement dc:rights
-
- info:eu-repo/semantics/openAccess
- Language dc:language
- eng