The correct option is Basophils.
Explanation
White blood cells (Leukocytes) are essential components of the immune system. In a healthy human adult, the relative abundance of different types of leukocytes is determined through a Differential Leukocyte Count (DLC). These cells are broadly classified into granulocytes (neutrophils, eosinophils, basophils) and agranulocytes (lymphocytes, monocytes).
Detailed Analysis:
- Basophils: These are the least abundant white blood cells, constituting approximately 0.5% to 1% of the total leukocyte count. They are involved in inflammatory reactions and secrete substances like histamine, serotonin, and heparin.
- Neutrophils: These are the most abundant white blood cells, making up about 60% to 65% of the total count. They are phagocytic cells that destroy foreign organisms entering the body.
- Lymphocytes: These are the second most abundant leukocytes, accounting for roughly 20% to 25% of the total count. They exist as B-lymphocytes and T-lymphocytes and are responsible for immune responses.
- Erythrocytes: These are Red Blood Cells (RBCs), not white blood cells. While they are the most abundant cells in the blood overall, they do not fall under the category of leukocytes asked in the question.
Key Takeaway:
The decreasing order of abundance of white blood cells in human blood is: Neutrophils > Lymphocytes > Monocytes > Eosinophils > Basophils. (Mnemonic: Never Let Monkeys Eat Bananas).