HIV researchers have lengthy been making an attempt to establish the particular cells that the virus prefers to contaminate and conceal in. They know that HIV favors a particular kind of immune cells referred to as reminiscence CD4 T cells. However these cells are available many flavors, and it has been troublesome to establish precisely what makes one kind of reminiscence CD4 T cell extra enticing to HIV than one other.
For years, Gladstone Affiliate Investigator Nadia Roan, PhD, and her group have tackled this query by analyzing CD4 T cells based mostly on the gathering of proteins they bear on their floor. Lately, they set their sight on one other kind of molecule on the cell’s floor: sugars.
Roan teamed up with Mohamed Abdel-Mohsen, PhD, an affiliate professor at The Wistar Institute and a specialist within the mobile equipment that synthesizes sugars. Collectively, the scientists uncovered surprisingly completely different sugar patterns on completely different immune cells, and an intriguing interaction between HIV and the sugars coating CD4 T cells. They report their findings within the journal eLife.
“One of the crucial placing findings from our examine is that the quantity of a single kind of floor sugar can distinguish between reminiscence CD4 T cells with vastly completely different organic options and susceptibility to HIV an infection,” says Roan, who can also be an affiliate professor of urology at UC San Francisco and the examine’s co-senior writer.
The work additionally showcases a brand new method for learning particular person cells from massive populations that might result in a extra detailed image of mobile range.
“There’s a great range of cell-surface sugars,” says Abdel-Mohsen, co-senior writer of the examine. “However they’ve been understudied, partially as a result of they’re tougher to trace than proteins. By sorting massive populations of cells based mostly on each their sugar and protein profiles, we might uncover new lessons of cells which have eluded earlier research and will maintain the important thing to fixing necessary organic issues.”
Surveying the Sugars Coating Particular person Cells
The researchers studied varied chains of easy sugar molecules. The chains differ in size, branching patterns, and the kind of sugars they include, and are recognized to have an effect on quite a lot of cell properties.
“We questioned to what extent cell-surface sugars would possibly assist us inform aside various kinds of cells inside a inhabitants of immune cells,” says Tongcui Ma, PhD, the examine’s first writer and a scientist at Gladstone.
To reply this query, Roan’s group tailored a way referred to as CyTOF, which they beforehand used to review the protein profile of particular person immune cells. CyTOF depends on antibodies to establish particular proteins, and may document the presence, absence, and quantity of almost 40 completely different proteins without delay. On this examine, the group changed 5 of the CyTOF antibodies with 5 completely different lectins, molecules that may acknowledge varied sorts of sugars.
“We do not have as many lectins as we have now antibodies,” says Abdel-Mohsen. “However we all know of a number of lectins that may distinguish between a wide range of sugars with completely different shapes and molecular compositions, and we plan to broaden our work by utilizing new lectins sooner or later.”
With the modified CyTOF, which they named CyTOF-Lec, the scientists analyzed immune cells from the blood and tissues of human donors. They discovered that the sample of sugars differed relying on the place the cells got here from-;blood versus tonsil versus the reproductive tract-;and what kind of immune cells they were-;CD4 T cells versus different T cells versus antibody-producing B cells.
“We now have an excellent toolkit to investigate in nice element the mix of proteins and sugars current on single cells,” says Roan. “And since all cells within the physique carry sugars at their floor, we imagine CyTOF-Lec can be helpful for the broader biomedical analysis discipline.”
HIV’s Candy Tooth
Inspired by this discovering, the scientists subsequent utilized CyTOF-Lec to CD4 T cells that that they had first uncovered to HIV within the lab. Not all CD4 T cells turn into contaminated by HIV, and Roan’s group and others through the years have uncovered some protein patterns that assist establish probably the most prone cells.
The scientists additionally know that after getting into a cell, HIV adjustments the proteins that the cell places on its surface-;a phenomenon referred to as viral reworking. Roan’s group has developed a bioinformatics software referred to as PP-SLIDE to reconstruct the profile of a cell earlier than it grew to become contaminated and transformed by HIV.
By combining CyTOF-Lec with PP-SLIDE, the group made two necessary discoveries.
First, HIV appeared to ideally infect the reminiscence CD4 T cells with the most important quantities of two sorts of sugars on their floor: fucose and sialic acid. Additional experiments confirmed that one in every of these sugars, sialic acid, is certainly required for HIV to effectively infect CD4 T cells.
Second, HIV additional boosted the manufacturing of those two sugars within the cells it had contaminated, indicating that reworking shouldn’t be restricted to proteins, however extends to sugars as effectively.
“It’s intriguing that there appear to be a number of mechanisms to make sure excessive ranges of sialic acid on contaminated cells: HIV’s bias towards cells with loads of sialic acid, and its skill to additional enhance floor sialic acid quantities,” says Roan. “This may increasingly assist HIV-infected cells survive, since sialic acid is related to evasion from immune surveillance.”
By escaping immune surveillance, these stealth contaminated cells might enable HIV to rapidly take maintain and unfold to extra websites within the physique. They could additionally signify good therapeutic targets.
HIV additionally hides from immune defenses by settling inside some cells in a principally silent type. These silent, or “latently,” contaminated cells are troublesome to eradicate as a result of it has to date been unimaginable to differentiate them unambiguously from non-infected cells. Roan’s group now plans to use CyTOF-Lec to samples from individuals residing with HIV, wherein these cells persist even within the presence of antiretroviral remedy.
“In doing so, we’d uncover sugar-based biomarkers that could possibly be used to focus on and eradicate these latently contaminated cells,” says Roan.
In fact, these tantalizing hypotheses will must be examined with extra experiments. However the findings to date set up CyTOF-Lec as a promising new software to uncover new cell biology, together with the function of sugars in an infection by viruses apart from HIV, reminiscent of SARS-CoV-2 and influenza.