What kind of treatment are you using on the cells, and what kind of cells are you working with? I work with primary human skin cells and I have used pharmacological inhibitors of different kinases alone or in combination with UV radiation or known paracrine factors of the skin. I have frequently noticed that the cells treated with the inhibitor (alone or in combination with other treatments) have increased side scatter compared to cells without the inhibitor. Usually I run Annexin V/PI to look at cell death, but the increase in side scatter has no correlation with cell death. It is possible that the cells are undergoing autophagy and that the increase in granularity is due to increased autophagosome formation.

Thank you for your reply, Anne. I am also using primary skin cells, specifically fibroblasts. I'm using a not-well-characterized but data-supported SOD-1 inhibitor. While probing for ROS generation, which was confirmed, an increase in granularity was obvious between treated and control cells. Annexin V was definitely at the top of my list simply to clarify if an apoptotic event was occurring. I am curious what else could be happening and what methods others use to investigate side scatter 'morpholgy.'

Stress-induced (UV/chemical/ROS) injury might lead to increase cell size & granularity.

Senescence associated heterochromatic foci (SAHF) might also result in granularity increase. We have got early clues in this regard.

Please see the following publication from our group: Figure 7; Reproductive Toxicology 30 (2010) 377–386, wherein we have reported increase in cell size following exposure to NSNM.

Article Molecular mechanisms of isocyanate induced oncogenic transfo...

Hi Anne, could you send me a reference about autophagy associated with granularity? 

Hi Annielle,

Since I work in primary human skin cells, here's a paper focusing on keratinocyte autophagy and how that demonstrates increased granularity. Hope that helps.