Whole blood cultures
Immunopharmacology and immunotoxicology
The functionality of the human immune system is based upon an intricate network of positive and negative feedback signals between the different leukocyte (sub-)populations. Each of the different cell types secretes and reacts to a whole variety of messenger substances (cytokines, chemokines, lipid mediators, radicalized substances, etc.).
Only cell culture models representing the whole spectrum of immune cells can be regarded sufficiently predictive of the drug activity profile that has to be expected in vivo. This is why HOT Screen GmbH uses whole blood models wherever possible.
Drugs (not only immuno-suppressors, but also ion-channel blockers, enzyme inhibitors, receptor antagonists, antibiotics or anti-viral compounds) can interfere with this regulatory network in a positive or negative manner, hereby changing the course of immune cell activities sometimes dramatically.
Knowing such effects of newly developed drugs enables a precise definition, often even an extension, of their potential clinical applications. Substances exhibiting doubtful effects may be eliminated from the R&D pipeline at an early stage or modified chemically to achieve the desired safety. The use of HOT Screen test models will accelerate the substance development process considerably.
Whenever testing the performance of leukocytes from volunteers or patients it has to be kept in mind that all procedures used to isolate immune cells will generate changes in their activity profile. This can lead to artificial shifts in drug effects to be observed in such test systems.
Another drawback of cultures of isolated leukocytes, or – even worse – sub-populations hereof, is that these cells are only able to set up a fraction of the multi-layered signalling network required for a sufficient inter-cellular communication (compared to in vivo).
Moreover, even the smallest (and in most instances almost completely neglected) "cellular" elements of the blood, the platelets, contribute substantially to this messaging network. They not only secrete arachidonic acid metabolites (prostaglandins, leukotrienes, lipoxins, etc.), but also modify the expression of important activating receptors on leukocytes.
Not less important, the availability of biologically active cytokines in the cultures is strongly modified by enzymes released from activated neutrophil granulocytes.
Last, but not least, also red blood cells contribute to the development of an in vivo like condition by forming buffer surfaces for excess mediators.
These examples demonstrate clearly the importance of having all active elements of the blood present in experimental cultures. Only this way artificial findings can be avoided. This is particularly true in the pre-clinical and clinical evaluation of immunologically active drugs (anti-inflammatory substances, immunosuppressors, immunomodulators, adjuvants, vaccines etc.).
Another critical issue in the experimental detection of cytokines is the choice of methods by which this is accomplished. Despite the wide spread use of mRNA based technologies to detect cytokines, it is highly important to mention that the amount of mRNA of a given cytokine does not necessarily reflect that of the secreted mediator. Lots of post-transcriptional events modify the nature as well as the amount of mediators released in the end.
In addition, a whole range of other mediators cannot be detected at the RNA level (histamine, lipid mediators, reactive oxygen products, ATP, peptide hormones released from pre-formed precursors, etc.).
Therefore, whole blood cultures, combined with a thorough selection of endpoint measurement systems represent the best available tools for an optimized substance profiling. The high degree of complexity in these signalling networks is matched at HOT Screen GmbH by using multiplexed protein bioarray tests and other assays.