Leukocytes, commonly known as white blood cells, are essential cells for defending the body against foreign agents such as bacteria, viruses, and parasites.
They are produced in the bone marrow and circulate in the blood, performing various roles within the immune system. There are five main types of leukocytes:
Neutrophils
These constitute the first line of defence against bacterial infections. When an infection occurs, the bone marrow increases neutrophil production, which act through phagocytosis, eliminating invading microorganisms.
Eosinophils
They are involved in defence against parasites and also participate in allergic reactions, producing substances that intensify the inflammatory response.
Basophils
Although few in number, they are important in inflammatory and allergic responses. They release histamine and other substances that promote the dilation of blood vessels, facilitating the arrival of other white blood cells to the site of infection or inflammation.
Lymphocytes
These are essential for the adaptive (or acquired) immune response, which develops throughout life, and include two important cell types:
B lymphocytes: responsible for producing antibodies that recognise and neutralise microorganisms.
T lymphocytes: destroy virus-infected and tumour cells, as well as coordinate the immune response.
Monocytes
These are large cells that, upon entering tissues, transform into macrophages. Their main function is phagocytosis (ingesting) of microorganisms and the removal of dead cells, contributing to tissue repair.
Leukocytes play a crucial role in protecting the body, acting in a coordinated manner to combat infections, parasites, and respond to allergies or inflammation. Understanding the different types and functions of these white blood cells helps to better comprehend how the body maintains its natural defence and emphasises the importance of regular blood tests to monitor health and detect changes early.
The main diseases related to leukocytes are conditions that cause either an increase in their blood levels (leukocytosis) or a decrease (leukopenia). Leukocytosis may indicate infections, inflammations, and more serious conditions such as leukaemia and lymphoma, while leukopenia can be caused by infections, autoimmune diseases, bone marrow disorders, and chemotherapy.
The specialist best suited to advise on and treat blood disorders and their components, such as leukocytes, is the haematologist.
15, October 2025
