Stefanie Heidemann

Home Institution
Westfälische Wilhelms-Universität Münster

Host Institution(s)
Inflammatory Bowel Disease Center, Cedars-Sinai Medical Center, Los Angeles, CA
Research Mentor: Stephan R. Targan, M.D.

E-Mail:
 heidems@yahoo.com

Research Topic
see Abstract
Personal Reactions to the U.S. Experience
I very much enjoyed the opportunity of doing research at the IBD Center. I got involved in an interesting research project and was encouraged to work independently. Nevertheless, I received every support I needed. It was a highly enriching experience to do research on such a professional level, in the midst of enthusiastic scientists.
Los Angeles is a very cosmopolitan city. I got to know people from all over the world and from very different social backgrounds. Working in a lab at the Cedars-Sinai Medical Center in Beverly Hills, I saw lots of people living in splendor and glory. Visits to downtown LA, where the streets are the homes of the less fortunate, highlighted, however, that getting a career and earning one's living in the United States can often be a struggle.
Greatest Difficulties Encountered
Getting around without a car in a city where everybody depends on his (own) car to an extent that there are many incentives to encourage car-pooling (e.g. car-pool lanes on highways and free parking for car-pooling employees at the Cedars-Sinai Medical Center) turned out to be quite an obstacle, especially during the MTA strike in October. I was very lucky to have a roommate owning a car, which facilitated trips to the supermarket and to the surroundings on the weekend.
I am currently working on finding a way to participate in a clinical rotation in a hospital here in Los Angeles, although I do not know yet if that will be possible. As I applied directly to the IBD Center for this research rotation, I have not been enrolled as a student at UCLA. The Cedars-Sinai Medical Center, however, only accepts medical students who have been assigned by the UCLA Medical School for clinical rotations.
Most humorous incident
During the MTA strike I had to go downtown to take the written test for the California driver's license. I took the Commuter's Express, which is run by a company not involved in the strike, to get there in the morning. That worked out well. On the way back, however, I got stuck. None of the buses going down Wilshire Blvd., was running. As 15 miles lay ahead of me, I decided against walking and eventually joined a small group of people at one of the otherwise deserted bus stops. They were mostly Mexicans trying to get a ride in a car driving down Wilshire Blvd. When finally a van stopped to pick us up, I did not hesitate to get in together with a couple of other people. That was the funniest trip of my life! Squeezed into the limited space of the van together with other stranded people and listening to high-volume salsa music I arrived safe and sound in Beverly Hills.

Helpful Hints for Future Students

  • When applying to your host institution be persistent. It pays! Do not hesitate to e-mail or call the person in charge to speed up the application procedures if you are running out of time.
  • Try to do the paperwork for the visa application as soon as possible.

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Abstract on Research Topic

Effect of TL1A on the cytotoxic activity of natural killer cells activated by IL-12 and IL-18

Authors:
Stephanie C. Heidemann, Carol J. Landers, John L. Prehn and Stephan R. Targan
Introduction and Purpose:
Crohn's disease is a chronic inflammatory disease of the gastrointestinal tract considered to arise from a dysregulated response of T helper 1 cells (TH1) to commensal bacteria. The cytokines IFN-g and TNF play a central role in the development of mucosal inflammation in Crohn's disease by initiating and amplifying TH1 polarization, which, itself, is characterized by high level IFN-g production. TH1 polarization is reinforced by the cytokines IL-12 and IL-18 which are also increased in the mucosa of patients with active Crohn's disease. TL1A is a new TNF-like factor that acts as a costimulator of IFN-g production by binding to the death domain-containing receptor DR3 on activated peripheral blood and lamina propria T cells. DR3 is not expressed on unstimulated T cells, but can be upregulated on a small proportion of T cells by TCR activation by IL-12 and IL-18. In contrast, up to 70% of NK cells express DR3 after stimulation by IL-12 and IL-18, but on these cells activation of DR3 by TL1A only increases IFN-g production by a modest two fold versus 3-15 fold seen in T cells. IL-12 and IL-18 are known to induce cytotoxic activity in NK cells. We hypothized that TL1A could also have an effect on the cytotoxic activity of NK cells stimulated by IL-12 and IL-18. The purpose of this study was to investigate whether TL1A affects the cytotoxicity of NK cells activated by IL-12 and IL-18 with regard to sensitivity and specificity towards target cells.
Material and Methods:
PBMC were isolated on Ficoll-Hypaque density gradients and depleted of monocytes by culture in flasks overnight. NK cells were isolated from the non-adherent PBL by magnetic cell sorting (negative selection). For maximal or submaximal activation NK cells (0.5 x 106 /ml) were cultured with a combination of high or low amounts of IL-12 and IL-18 for at least 24 hrs. TL1A was added to test wells at 50ng/ml. DR 3 expression in stimulated NK cells was measured by FACS. Enhancement of IFN-g production in response toTL1A was documented by IFN-g-ELISA. To measure NK cell cytotoxicity 51Cr-release assays were performed 3, 6, 21, 24 and 72 hrs after TL1A had been added. The lymphoblast cell lines K562 (NK-sensitive), Raji and Daudi (NK-resistant) were used so far as target cells.
Results:
Whereas DR3 expression could not be detected on unstimulated NK cells, DR3 was upregulated by low concentrations of IL-12 and IL-18. The DR3 pathway proved to be functional by enhancing IFN-g production two-fold in response to TL1A. However, TL1A did not affect the cytotoxicity of NK cells which had been submaximally or highly activated by IL-12 and IL-18 towards the for-mentioned target cell lines at any of the timepoints.
Conclusion:
The purpose of the strong upregulation of DR3 expression in NK cells by IL-12 and IL-18 remains unclear. Although TL1A did not affect NK cytotoxicity towards lymphoblast target cells, it could have an effect on the specificity of NK cytotoxic activity, e.g. the cytotoxicity against epithelial or fibroblast target cell lines. This will be tested.
TL1A could also serve to prolong maximal cytotoxicity in activated NK cells over a time period longer than that maintained by IL-12 and IL-18 alone. In addition to upregulating IFN-g expression DR3 engagement by TL1A could also regulate the transcription of other genes in NK cells which will be investigated by microarray analysis.