Today I Learned:
1) There is a human cytokine receptor called CCR5 which HIV uses to enter human immune cells. Individuals with homozygous knockout mutations in their CCR5 gene appear to be immune to HIV, and in a few rare cases, bone marrow replacement by CCR5-negative donors has cured individuals of AIDS. Today I learned that there is a non-HIV-related phenotype associated with CCR5 knockout -- CCR5-negative individuals are somewhat more succeptible to West Nile virus, and possibly other viruses. Specifically, they're just as likely to get infected by West Nile, but their clinical outcomes are worse once they're sick.
2) Speaking of CCR5, today I learned that a group of scientists from Wuhan University, China, have built a Cas9-knockout system for CXCR4, another cytokine receptor required by HIV. Their adenovirus-based system is pretty effective at removing CXCR4 from cultured cells, and seems to pretty much prevent HIV from infecting those cells.
3) How a Klein bottle is *actually* shaped. If you go buy a Klein bottle at any of the usual places, you'll get a jug where the handle passes back through the side of the jug and out the bottom, effectively putting the entrance to the bottle on its bottom. These are cool, but they're not *really* Klein bottles. A true Klein bottle doesn't intersect itself at all.
Here's how to imagine a real Klein bottle. Take a commercial Klein bottle. Consider the part where the handle intersects the body. Firstly, fill in the bit inside the handle so that the body has a complete, hole-less surface. Now grab the handle where it intersects the surface of the body and pull it out of plane in the 4th dimension a little bit -- this is similar to layout out a string so it crosses itself and pulling one of the threads out of plane in the 3rd dimension.
...and that's why nobody makes real Klein bottles.
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