Experiments – Done!! a.k.a. I Never Want to Do Immunohistochemistry Again

Those who have been following me the past month on Twitter have witnessed my countdown to leaving the NIH. For those reading my blog, apologies for not posting, but time was limited and there was a lot of work to be done. So I now post a recap:


I needed to make sure I had all the information necessary to create a coherent project. To this end, the main focus of the last month was making sure I had all the staining I needed from my transplants in order to correlate angiogenesis and good bone formation, so that I could justify my thesis.


To this end, a preliminary survey of all of the “good transplants” – ones that I had transplanted since my return to the states in 2010 was made. This meant that 180 slides were observed in H&E. It was found that a number of transplants were in fact mammary glands or plain brown fat. The explanation for this is that sometimes transplants are resorbed – one of the reasons, after all, why I focused on collagen-based scaffolds is because they are resorbed over time. However, the ideal would be for the scaffold to be resorbed but simultaneously replaced by bone. Since this does not always happen, I was occasionally hunting around in the mouse for anything that resembled a transplant. After the preliminary survey, samples that were not transplants, or which were transplants but for reasons unknown were very fragmented and deemed “impossible to section” were abandoned. This left about 130 samples.


Some of the remaining samples were re-stained, and all were scanned using an Aperio slide scanner. This is an amazing machine, which is the saving grace for someone like me – a graduate student who vehemently despises microscopy. Slides are scanned at 40x resolution and then the entire image can be viewed on a computer, zoomed, and images captured of any section desired – without having to constantly refer back to the actual slide. Also very handy for me because it meant all I had to bring to Oxford was my computer. Welcome to the digital age of science.


Finally, all of the 130 slides to be analyzed were graded for bone formation and hematopoiesis (marrow formation) on a scale of 1-4 by 3 “blinded” researchers. I use blinded in quotation marks here, since the identities of what the samples were clearly written on the slide, but I have a habit of using acronyms for anything, so no one knew what they were. As one of the “blinded” researchers myself, I simply didn’t look at the slides based on identities, but by their numbered position in the box – and, as they were not arranged in the most logical order, my gradings can also be seen as unbiased.


Some of the slides appeared to be either pre-osteoid (i.e. in the process of forming bone) or cartilage, so I stained with toluidine blue. However, none of these samples turned out to be cartilage. For grading purposes these samples were deemed unsuccessful.


Then, I came to what I had been dreading for months. Immunohistochemistry.


Often shortened to IHC, immunohistochemistry is simply the staining of sections of tissue for specific expression of markers through the use of antibodies. Sounds simple, but not all antibodies are created equal and it took me about 10 different antibodies to find one that was specific for blood vessels and worked on my sample. Adding to the complexity of this process is the need for heat retrieval of some markers – for which every company and scientist will tell you a different protocol. Yet another variable exists in how to show where you have specifically selected with your antibody (i.e. choice of a secondary antibody). Since most antibodies aren’t themselves fluorescent or colorful (chromogenic) this means that you have to create another layer of antibody by selecting for the first one with your secondary which is either fluorescent or colorful. Thus, I think it’s easy to see that what, in theory, could be a very simple process, is indeed a very complex one.


But, I got it to work. I finally got really good immunohistochemistry of blood vessels on 16 representative samples from one experiment. The rest of the samples I am going to have to attempt to count the blood vessels by eye based off the H&E staining scans that I have.


And then there was the hurricane. But that’s for my next post!


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