Do glucocorticoids raise circulating neutrophil counts while low cortisol causes neutropenia with eosinophilia?

Glucocorticoids play a central role in modulating the distribution and lifespan of white blood cells. Fluctuations in cortisol—whether from pharmacological administration or physiological deficiency—result in predictable and clinically significant changes in the peripheral blood count.

Clinical and effectiveness evidence

In clinical practice, the administration of glucocorticoids like prednisone or dexamethasone leads to a rapid increase in circulating neutrophils, often within hours. Conversely, states of hypocortisolism, such as primary or secondary adrenal insufficiency, are characterized by "relative" changes: a lower neutrophil count (neutropenia) and an increase in eosinophils (eosinophilia). Studies of patients with adrenal crisis or undiagnosed Addison’s disease frequently reveal these hematologic markers as diagnostic clues. Research shows that these abnormalities are highly reversible; for instance, eosinophil counts often normalize within 24 to 48 hours following the initiation of glucocorticoid replacement therapy.

Mechanistic explanations

The shifting of these cell populations is driven by distinct molecular pathways regulated by the glucocorticoid receptor:

• Neutrophil Demargination: Cortisol induces the shedding of L-selectin (CD62L) and inhibits the expression of adhesion molecules on both neutrophils and the vascular endothelium. This causes neutrophils in the "marginal pool" (those tethered to vessel walls) to release into the "circulating pool," effectively increasing the measurable count without a primary increase in production.
• Reduced Egress and Survival: Glucocorticoids inhibit the movement of neutrophils from the blood into tissues by disrupting chemotaxis and reducing F-actin polymerization. Simultaneously, they extend neutrophil lifespan by upregulating anti-apoptotic proteins like Mcl-1.
• Eosinophil Suppression: Cortisol acts as a potent pro-apoptotic signal for eosinophils. In low cortisol states, this inhibitory signal is removed, leading to increased eosinophil survival and higher circulating levels.

Bottom line

Glucocorticoids increase circulating neutrophils by releasing them from vessel walls and preventing their movement into tissues, while low cortisol levels typically lead to lower neutrophil counts and higher eosinophil levels due to the loss of these regulatory signals.