In the end, did the leukocytes primarily migrate paracellularly or transcellularly through the blood brain barrier? How else is TEM controlled? And, finally, what does this mean for neurological research in the future? 

​

​

Method of leukocyte migration (para vs. transcellular)

​

See experiments for a more detailed explanation of how leukocytes migrate across the endothelial cells of the blood brain barrier. 

​

Over 98% of leukocytes migrated paracellularly across the endothelium. When CCL2 (a leukocyte activator that encourages migration) was added, transcellular migration straight through the cell was up to 15% higher; however, under normal conditions with tightly packed endothelial cell as found in the blood brain barrier, transcellular migration rarely occurred.

​

The majority of leukocytes travel paracellularly through the blood brain barrier, or through the gaps in endothelial cells. 

​

​

​

Effect of PECAM-1 and CD99 (signaling molecules)

​

See experiments for a more detailed explanation of what PECAM-1 and CD99 are and how their affects on leukocyte migration were tested.

 

When PECAM-1 and CD99 weren’t blocked, leukocytes migrated through the endothelial cells at 90%, a normal rate for TEM. When they were blocked, however, leukocyte migration decreased to 15%-20%. These results were replicated in another cell line, TY10, that is found in the blood brain barrier.  

​

PECAM-1 and CD99 clearly play an important role in leukocyte migration through the blood brain barrier.

 

The implications of this could potentially lead to a treatment for neurological disorders that are linked to an abundance of leukocyte migration; halting TEM could lead to better outcomes in these diseases.

​

​

​

​

How tight junctions behave during TEM

​

See experiments for a more detailed explanation of how tight junctions behave during migration of leukocytes.

 

VE-Cadherin, another type of gatekeeping protein found at junctions between endothelial cells, is known to allow molecules through by moving out of the way and then reforming immediately after entry of molecule; the results of this experiment would indicate whether tight junctions do the same.

​

Labelling and viewing of claudin-5, which makes up tight junctions, showed that it disappeared as leukocytes traveled between endothelial cells just as cadherin does, implying that it too alters reforms itself to allow entry to molecules.

​

Tight junctions are plastic and reform themselves to allow leukocytes to travel through. 

​

​

​

​

​

​

​

                                                                                     *                      *                         *

​

​

​

​

​

Piecing together the results of these separate experiments points to one conclusion: the small gaps between endothelial cells in the brain do not cause leukocytes to migrate straight through the cell body. 

 

Rather, leukocytes migrate in between the cells, and tight junctions reform themselves to allow this passage. PECAM-1 and CD99, signalling molecules found in the blood brain barrier, were also found to be integral to leukocyte migration; blocking them decreases leukocyte migration drastically. 

​

If leukocytes are superheroes gone rogue, this could stop them in their path and prevent them from doing too much damage in the brain. However, remember why they were called superheroes in the first place- a healthy amount of leukocytes is necessary to fight infection in the brain and body. We'd need to walk this fine balance between preventing too many from entering the brain and allowing just enough through for them to do their jobs. 

​

However, if this balance is achieved, it might eventually be a treatment for neurological disorders that stem from an accumulation of leukocytes. This is not to say that stroke and multiple sclerosis could be solved in a day; instead, this experiment unveils one mystery of these disorders and might someday lead to unveiling the rest. 

​

​

​

​

​

​

​

​

​

​

​

​

​

​

​

​

​

​

​

​

​

​

​

​

​

​

​

​

​

​

​

​

​

​

​

​

​

​

​

​

​

​

​

​

​

​

​

​

​

​

​

​

​

​

​

​

​

​

​

​

​

​

​

​

​

​

​

​

​

​