Final Answer:
The five types of white blood cells (WBCs), in order of commonness, are neutrophils, lymphocytes, monocytes, eosinophils, and basophils.
Step-by-step explanation:
White blood cells, or leukocytes, play a crucial role in the immune system's defense against infections and foreign invaders. Neutrophils are the most common type of WBC and are highly effective in combating bacterial infections. Lymphocytes, including T cells and B cells, contribute to the body's immune response and the formation of antibodies. Monocytes function as phagocytes, engulfing and digesting pathogens. Eosinophils are involved in responses to allergic reactions and parasitic infections, while basophils release histamine and other substances in allergic responses. Understanding the relative abundance and functions of these WBC types is essential for assessing immune system health and diagnosing various medical conditions.