Neutrophilia, lymphopenia and myeloid dysfunction: a living review of the quantitative changes to innate and adaptive immune cells which define COVID-19 pathology
Codd AS., Hanna SJ., Compeer EB., Richter FC., Pring EJ., Gea-Mallorquí E., Borsa M., Moon OR., Scourfield DO., Ahern DJ., Almuttaqi H., Alonzi DS., Alrubayyi A., Alsaleh G., Bart VMT., Batchelor V., Bayliss R., Berthold DL., Bezbradica JS., Bharuchq T., Borrmann H., Borsa M., Borst R., Brun J., Burnell S., Capitani L., Cavounidis A., Chapman L., Chauveau A., Cifuentes L., Codd AS., Compeer EB., Coveney C., Cross A., Danielli S., Davies LC., Dendrou CA., Dimonte S., Durairaj RRP., Dustin LB., Dyer A., Fielding C., Fischer F., Gallimore A., Galloway S., Gammage A., Gea-Mallorquí E., Godkin A., Hanna SJ., Heuberger C., Hulin-Curtis S., Issa F., Jones E., Jones R., Ladell K., Lauder SN., Liddiard K., Ligoxygakis P., Lu F., MacLachlan B., Maleki-Toyserkani S., Mann EH., Marzeda AM., Matthews RJ., Mazet JM., Milicic A., Mitchell E., Moon O., Nguyen VD., O'Hanlon M., Pavillet CE., Peppa D., Pires A., Pring E., Quastel M., Reed S., Rehwinkel J., Richmond N., Richter FC., Robinson AJB., Rodrigues PRS., Sabberwal P., Sami A., Peres RS., Sattentau Q., Schonfeldova B., Scourfield DO., Selvakumar TA., Shepherd FR., Shorten C., Simon AK., Smith AL., Crespo AT., Tellier M., Thornton E., Uhl LFK., van Grinsven E., Wann AKT., Williams R., Wilson JD., Zhou D., Zhu Z., Gallimore AM., Milicic A.
Abstract Destabilization of balanced immune cell numbers and frequencies is a common feature of viral infections. This occurs due to, and further enhances, viral immune evasion and survival. Since the discovery of the Severe Acute Respiratory Syndrome coronavirus 2 (SARS-CoV-2), which manifests in coronavirus disease 2019 (COVID-19), a great number of studies have described the association between this virus and pathologically increased or decreased immune cell counts. In this review, we consider the absolute and relative changes to innate and adaptive immune cell numbers, in COVID-19. In severe disease particularly, neutrophils are increased, which can lead to inflammation and tissue damage. Dysregulation of other granulocytes, basophils and eosinophils represents an unusual COVID-19 phenomenon. Contrastingly, the impact on the different types of monocytes leans more strongly to an altered phenotype, e.g. HLA-DR expression, rather than numerical changes. However, it is the adaptive immune response that bears the most profound impact of SARS-CoV-2 infection. T cell lymphopenia correlates with increased risk of intensive care unit admission and death; therefore, this parameter is particularly important for clinical decision-making. Mild and severe diseases differ in the rate of immune cell counts returning to normal levels post disease. Tracking the recovery trajectories of various immune cell counts may also have implications for long-term COVID-19 monitoring. This review represents a snapshot of our current knowledge, showing that much has been achieved in a short period of time. Alterations in counts of distinct immune cells represent an accessible metric to inform patient care decisions or predict disease outcomes.