For the past 4 years of my life I have studied cytokine signalling, and more specifically the JAK-STAT signalling pathway. Over the course of the COVID-19 pandemic, cytokine signalling has been increasingly on other peoples minds too. Some cytokines are important for immune responses, however in COVID-19 the production of these cytokines occurs in excess and can lead to what we call cytokine storm. During cytokine storm, excessive or uncontrolled levels of cytokines are released in the body, and these cytokine activate the immune system further, which leads to excessive inflammation and ultimately this can be lethal.
So what are cytokines?
Cytokines are small proteins (like little machines made by your cells) that are made by all different types of cells. These cytokines are particularly important in our immune and haematopoietic (blood) systems They are essentially little messages that our cells send to one another to tell them what to do, or how to respond to something like a viral pathogen. The term “cytokine” arises from the Greek κύτος and κίνησις (cell and movement) consistent with their ability to mobilize cells to sites of infection and inflammation.
But how do they work?
Cytokines as i mentioned are proteins, and they bind to and activate other proteins in cells. This is what we call a signalling cascade. In the case of cytokines they bind to receptors on the surface of cells, and these receptors transmit the signal from outside the cell to the inside via the activation of three main signalling pathways; The JAK-STAT pathway, the MAPK pathway and the PI3K pathway. These pathways promote cell proliferation, survival and growth (see image below) by upregulating different genes in the cells.
If you are interested in learning more I would encourage you to check out our review on the topic, linked below (Morris et al., 2018):
Morris, R., Kershaw, N.J., and Babon, J.J. (2018) The molecular details of cytokine signaling via the JAK/STAT pathway. Protein Science 27: 1984-2009.