What are Neutrophils?
Neutrophils are by far the most common leukocytes (white blood cells) in the body and as such they form part of the innate immune system, the body’s first defense against invasions of foreign pathogens [1, 2, 3, 4, 5, 6, 7, 8, 9].
What do Neutrophils do?
Neutrophils are professional phagocytes, meaning they can eat and kill harmful microorganisms like bacteria and fungi. They are highly mobile and are recruited to sites of inflammation or infection [2, 3, 4, 5, 6, 7, 8, 9].
When they reach the site of infection, neutrophils can kill microbes by phagocytosis (digestion of ingested microbes), reactive oxygen species (chemicals that can kill microbes), antimicrobial peptides (proteins of 12-100 amino acids that can punch holes in the microbial membrane to destroy microbes), and neutrophil extracellular traps (NETs; web-like structures made of chromatin (DNA and histones) that can trap and kill microbes) [2, 3, 4, 5, 6, 7, 8, 9].
Neutrophils also have an anti-inflammatory side, working to regulate immune response by releasing cytokines (endocrine signals) modulating immune activity, and interacting with other immune cells such as macrophages or dendritic cells, to modulate their activity and the overall immune response [1, 2, 3, 4, 5, 6, 7, 8, 9].
What are the Causes of High Neutrophil Counts?
High neutrophil counts, a condition known as neutrophilia, can be caused by a variety of factors and underlying conditions.
One of the most prevalent causes of increased neutrophil counts is infection, particularly bacterial infections – with neutrophils increasing when the immune system is trying to fight off intruder bacteria [10].
Other pathways that upregulate neutrophil counts include noninfectious inflammation because neutrophils are part of an immune response and are made in greater abundance in the presence of systemic inflammation [10].
Physical injury and surgery can cause elevated neutrophil counts: this is in part due to damage to the tissues of an organism, triggering an immune response that includes neutrophil production [10].
Certain lifestyle factors can cause elevated neutrophil counts, the most common being cigarette smoking or sniffing tobacco; high stress; and overtraining. All of these can ramp up immune system stimulation and raise neutrophil production [10].
Some drugs, such as steroids, are also known to cause high neutrophil values. Steroids stimulate a rise in neutrophils [10].
Serious health conditions, such as heart attack or chronic myeloid leukemia, can also increase neutrophil counts. In either case, the organism responds to injury or illness by growing more neutrophils to protect itself [10].
In some circumstances, high neutrophil figures can be a symptom of a disorder called chronic idiopathic neutrophilia (CIN). In this condition, the neutrophil count remains elevated for months or even years, in conjunction with a seemingly unexplained hyperactive immune response [11].
High Neutrophil Counts during Pregnancy
Neutrophils, one of the various types of white blood cells (called leukocytes), are critically involved in the maternal immune response to pregnancy. The number of these cells increases modestly with advancing gestation, suggesting that they compensate, at least in part, for the general immunosuppression of gestation [12].
Do High Neutrophil Counts Influence Pregnancy?
Levels of superoxide anion (O) and nitric oxide (NO) released by neutrophils have been measured in pregnant women and are reported as being increased in the early second trimester of pregnancy [13]. However, superoxide anion production was reduced in pregnant versus non-pregnant controls [14].
However, neutrophil depletion in early pregnancy is also associated with poor blastocyst implantation, indicating that neutrophils are also important early in pregnancy [15].
Increased neutrophil levels have also been linked to gestational diabetes mellitus (GDM). Results from one study showed that participants in the highest neutrophil count tertile compared with the lowest tertile had a 1.85-fold higher risk of developing GDM [16]. Another study showed that the first-trimester neutrophil count was strongly related to the development of GDM and poor perinatal outcomes [17].
Conclusion
In conclusion, higher neutrophil counts can lead to a different pregnancy pathway, altered immune responses, foetal implantation and increased risk of GDM but more research is required yet to explain the role in the pregnancy.