# Neutrophils Neutrophils are a type of white blood cell that play a crucial role in the immune system's defense against invading pathogens (Silvestre-Roig et al., 2016). They are part of the innate immune system and are responsible for phagocytosing, killing, and digesting bacteria and fungi (Segal, 2005). Neutrophils were previously believed to kill microbes through the production of oxygen free radicals and reactive oxygen species generated by the NADPH oxidase, as well as oxidized halides produced by myeloperoxidase (Segal, 2005). However, recent research has shown that this understanding is incorrect (Segal, 2005). Low levels of neutrophils in the blood, known as neutropenia, can have various causes and can lead to an increased susceptibility to infections (Silvestre-Roig et al., 2016). Symptoms of low neutrophil levels may include recurrent infections, fever, mouth sores, and skin abscesses (Silvestre-Roig et al., 2016). Neutropenia can be caused by a variety of factors, including certain medications, chemotherapy, radiation therapy, autoimmune diseases, and bone marrow disorders (Silvestre-Roig et al., 2016). It is important to identify the underlying cause of neutropenia in order to determine the appropriate treatment. To increase neutrophil levels, the underlying cause of neutropenia needs to be addressed. This may involve discontinuing medications that are causing neutropenia, treating underlying infections or autoimmune diseases, or using medications to stimulate the production of neutrophils (Silvestre-Roig et al., 2016). In some cases, a blood or bone marrow transplant may be necessary to restore normal neutrophil levels (Silvestre-Roig et al., 2016). Further questions that can be asked about neutrophils include their role in homeostasis and disease, their phenotypic and functional heterogeneity, and their involvement in innate and adaptive immune responses (Silvestre-Roig et al., 2016). Additionally, understanding how neutrophils kill and degrade microbes can provide insights into their integrated role in the immune system (Nauseef, 2007). Low neutrophil levels can indicate that attention should be paid to potential underlying causes and the risk of infections. It is important to monitor neutrophil levels and work with a healthcare professional to determine the appropriate course of action (Silvestre-Roig et al., 2016). -- Vitamin B3 [[niacin]], also known as nicotinamide or niacin, has been studied for its potential effects on neutrophils and their function. Several studies have investigated the role of vitamin B3 in modulating neutrophil activity and its impact on various conditions. One study found that vitamin B3 treatment could enhance the killing of Staphylococcus aureus, a bacterium, through a myeloid-specific transcription factor (Paruch et al., 2022). Additionally, vitamin B3 was shown to be efficacious in both prophylactic and therapeutic settings (Paruch et al., 2022). Another study demonstrated that vitamin B3 treatment significantly inhibited neutrophil infiltration into the lungs and elicited a strong anti-inflammatory effect during ventilator-induced lung injury (Chauhan et al., 2020). However, it is important to note that vitamin B3 treatment in this context paradoxically led to the development of significant hypoxemia (Chauhan et al., 2020). Furthermore, vitamin B3 has been reported to reduce neutrophil infiltration into the lungs, thereby reducing inflammation (Chauhan et al., 2020; Kouhpayeh, 2022). This anti-inflammatory effect of vitamin B3 may have implications for conditions involving excessive neutrophil activation and inflammation. It is worth mentioning that vitamin B3 is involved in various cellular processes and has multiple functions beyond its potential effects on neutrophils. It acts as a coenzyme in many reactions and plays a role in cell energy metabolism, redox reactions, and DNA repair (ZHANG et al., 2023; Wu et al., 2022). Vitamin B3 has also been associated with neuroprotection, antioxidant activity, and modulation of inflammatory responses (Wu et al., 2022). While the studies suggest potential benefits of vitamin B3 in modulating neutrophil function and reducing inflammation, it is important to note that the effects of vitamin B3 can be complex and context-dependent. Further research is needed to fully understand the mechanisms and clinical implications of vitamin B3 on neutrophils and immune responses.