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Report

Teaser, summary, work performed and final results

Periodic Reporting for period 1 - ImmProDynamics (Dissecting the interplay between the dynamics of immune responses and pathogen proliferation in vivo)

Teaser

Summary

Many infectious microorganisms can invade into cells of the body in order to hide from the defence mechanisms of the immune system. Some microbes can not only survive, but even grow to high numbers within infected cells. It is unknown if, or by which mechanism, the immune system is able to specifically detect microbes which are growing, which would be a very important information to identify a threat by such intracellular microorganisms.

The question whether and how the immune system perceives growth of a microorganism is important regarding the fact that vaccines containing live microbes exhibit dramatically different outcomes of immune protection. Also, slow growing pathogens play important roles during chronic infections and the establishment of resistance to antibiotic treatment. Therefore, understanding how the growth rate of infectious microbes is linked with the behavior of immune cells could provide critical information on how infections can be controlled, and how microbial persistence in the body and antibiotic resistance could be counteracted.

In order to elucidate how immune cells could sense growth of an infectious organism, we are using a biosensor that permits measuring the growth rate of the microbe Leishmania major in real-time and in the ongoing infection. This enables us to determine whether fast versus slow growing Leishmania occupy different cellular niches in the infected individual, and whether immune cells show a differential behavior when confronted with microbes of different growth rates. Also, we will manipulate the growth rate of the microbes in the ongoing infection to test whether such a manipulation changes the responsiveness fo the immune system. Finally, we will determine whether molecular activation signals in immune cells are differentially induced by fast versus slow growing microbes.

Work performed

In the first reporting period of the project, we have characterized the cell type in which growth of Leishmania major takes place predominantly in the infected skin: Using intravital 2-photon imaging of the tissue infected with Leishmania major that expresses a biosensor for growth, we could determine that the growth rate of the pathogen is strongly linked to specific cell types. We characterized these cell types using a multiparameter microscopy approach and flow cytometry and have identified one cell type as a niche for fast growing Leishmania major, but also as a reservoir from which the microbes can spread and infect new cells. These results have been recently accepted for publication at the journal PLoS Pathogens.

Furthermore, we have established a protocol to isolate single infected cells and compare them according to the growth rate of the Leishmania major within them. We are currently determining whether there are changes in the genes that are expressed within these cells linked to whether a specific cell is infected by fast or slow growing microbes.

Final results

Our experiments so far have for the first time defined the in great detail cellular environment in which Leishmania major grows efficiently. We have also been able to show in the ongoing infection the spread of the microbe from one cell to the next, which strongly contributed to the understanding of how infectious organisms can persist and disseminate at the site of infection.

The signaling pathways that we aim at identifying via isolation of single cells infected with fast versus slow growing microbes should yield important information on how cells of the immune system detects and reacts to high proliferation of an infectious organism. We will, after identification of candidate signaling molecule involved in this detection, test the influence on the immune system if such a molecule is lacking. This should give important insights in how the immune system could be manipulated in order to better protect against infections.