From the Guidelines
Steroids significantly suppress monocyte function and numbers in the bloodstream, and their use should be carefully considered to balance the benefits of reducing inflammation with the potential risks of immunosuppression, particularly in the context of infections like COVID-19 1. When administered, steroids like prednisone, dexamethasone, or methylprednisolone cause a decrease in circulating monocytes through several mechanisms. They inhibit monocyte production in the bone marrow, reduce their release into circulation, and promote their redistribution to tissues like lymph nodes and bone marrow.
- Steroids also impair monocyte functions by suppressing their ability to produce inflammatory cytokines,
- decreasing phagocytosis (their ability to engulf pathogens),
- and reducing their antigen-presenting capabilities. This immunosuppressive effect is why steroids are useful in treating inflammatory and autoimmune conditions, as they dampen the inflammatory response that monocytes help coordinate. However, this same effect explains why long-term steroid use can increase infection risk, as it compromises the immune system's ability to respond to pathogens. The impact on monocytes begins within hours of steroid administration and can persist throughout treatment, as noted in studies on their use in conditions like community-acquired pneumonia 1. In the context of COVID-19, the use of low-dose steroids has been explored for its potential to reduce the severity of the disease by mitigating the inflammatory response, with some evidence suggesting a beneficial effect in severe cases 1. However, the decision to use steroids should be made cautiously, considering the potential for increased risk of secondary infections and the need for careful monitoring of patients, as highlighted by guidelines and studies on the management of severe infections 1.
From the Research
Effects of Steroids on Monocytes
- Steroids, such as corticosteroids, have been shown to impair the function of monocytes, a type of white blood cell involved in the immune response 2.
- Specifically, high-dose corticosteroid therapy has been found to reduce the ability of monocytes to kill certain bacteria and fungi, such as Staphylococcus aureus and Candida tropicalis 2.
- However, this impairment is temporary, and monocyte function returns to normal levels 48 hours after the last dose of prednisone 2.
Mechanisms of Steroid Action on Monocytes
- Glucocorticoids, a type of steroid, have been found to affect monocytes and macrophages, another type of immune cell, by down-regulating pro-inflammatory mediators and inducing anti-inflammatory mediators 3.
- Steroids can also induce the differentiation of anti-inflammatory monocytes, which have an increased ability to migrate towards inflammatory stimuli and remove danger signals 3.
- The anti-inflammatory actions of steroids involve the repression of cytokine gene transcription and the direct interaction between the glucocorticoid receptor and other transcription factors activated in chronic inflammation 4.
Clinical Significance
- The association between steroid administration and monocytosis, an increase in monocyte count, is less common and the mechanism is not as well understood 5.
- However, corticosteroids have been found to have anti-inflammatory and immunomodulatory properties, which can be useful in regulating immune responses and treating inflammatory diseases 6.