Stepping into the field of physiology was not something I took lightly. It was largely intimidating; hugely intimidating, in fact, especially given that I came from a microbiology background! When the option came for me to exercise my knowledge of virology in my Honours year, I jumped at the opportunity.
Research had already been widely conducted on HIV and sleep in other parts of the world. Indeed, with the success of highly active antiretroviral therapy (ART), HIV has increasingly taken the position as a chronic illness. And in fact, quality of life aspects have become more prominent as HIV-related life expectancy has increased. As more was discovered elsewhere, it was a shame for me to realise that not much research on sleep and HIV was being done here in South Africa. So that is where I fitted myself in – well, my supervisors created this niche, but for the purposes of this story I’ll say that I inserted myself.
During my Honours year, I had run a cross-sectional study in a treated HIV cohort of South African patients, which unexpectedly revealed a relationship between higher CD4 counts and poorer sleep quality. Just to give some background, having a low CD4 count is one of the markers of AIDS, and the aim of ART is, by various means, to increase CD4 counts.
This relationship was seemingly counterintuitive, because one would expect there to be better sleep quality with better immune status (higher CD4 counts), as has been shown in studies in other countries, which found that lower sleep quality was associated with lower CD4 counts. Our cohort at the time differed from other studies’ cohorts as our patients had started ART later in their disease and their baseline CD4 counts were very low. We then hypothesized that during immune reconstitution, there may have been an increased immune activation in these patients, which may explain why the higher CD4 counts were associated with worse sleep quality. So we designed a longitudinal study to see how sleep quality progressed from an ART naïve state, up until a few months on treatment. In this longitudinal study, surprisingly, we found that patients did not complain about their sleep per se but seemed to start off with high daytime sleepiness which reduced (got better) across the study. In this new study, we found no relationship with CD4 counts and sleep quality, but instead found that people who had low viral loads at the time of initiation onto ART had worse sleep than those who had high viral loads.
So what happened between my honours and my masters research studies?
First of all, my cross-sectional study patients had been diagnosed for seven years and treated on average for four years, very different from the longitudinal cohort who had just been put on treatment and for whom we had followed up ‘only’ until the 18th month, though it is possible that sleep disruption occurs after our cut-off time period. Second, as mentioned before, patients in my cross-sectional study had started their treatment late in the disease when CD4 counts had dropped below 100 cells/μl (AIDS is defined by <250 CD4 T cells/μl and below 100 cells/μl, there are higher chances of developing immune reconstitution inflammatory disease when put on ARV treatment). In our longitudinal cohort, the guidelines had changed and patients started ARVs on average around 250 CD4 counts/μl. So it is possible that what we observed in the first study was a unique effect of starting treatment so late. In fact, current ‘reservoir’ studies (which follow HIV infection in CD4 memory T-cells) show that immune reconstitution is associated with a higher HIV reservoir load in CD4 memory cells. It is also associated with CD4 activation when treatment was started at lower CD4 counts, while there is nearly no HIV reservoir and very low CD4 activation when treatment is started when CD4 counts are still above 500 cells/μl.
And what about this new finding on the relationship between viral load and daytime sleepiness?
Currently we postulate that there is an underlying immune-mechanism affecting sleep quality. Indeed cytokines such as TNFa, Il-6, and Il1 have been shown to affect sleep quality. It may be that those who showed lower viral loads may have had a higher immune response against HIV, with concomitant higher production of cytokines, which may have led the patients to experience higher daytime sleepiness. Conversely, those with high viral loads may be those who are not able to build such a strong immune response and would have lower cytokine secretion, leading to lower daytime sleepiness. So my next step is to perform some cutting-edge (not-really) totally awesome (yes, really) cytokine analyses (actually I just ran it last week!) and flow cytometry, assessing the different activation of the CD4 T-cells as people start treatment up until over a year on treatment and investigate its association with sleep measurements. As you can see from the picture below, I’m already on the task of telling the T-cell’s story.
Believe me, nobody is more excited than me to find out what the answer is… but we’ll have to wait and see. On to PhD!!