Consider the statement: “Myeloid stem cells give rise to all leukocytes (white blood cells).” How should this statement be classified?

Introduction / Context:
Blood cell formation, or haematopoiesis, takes place mainly in the bone marrow and involves several types of stem cells. White blood cells (leukocytes) are a diverse group that includes granulocytes, monocytes and lymphocytes. To understand diseases of the blood and immune system, it is important to know which stem cell lineages give rise to which types of leukocytes. This question asks you to evaluate the correctness of a statement claiming that myeloid stem cells give rise to all leukocytes.

Given Data / Assumptions:

The statement under evaluation is: “Myeloid stem cells give rise to all leukocytes.” We know that leukocytes are white blood cells, including granulocytes, monocytes and lymphocytes. Options allow us to classify the statement as correct or incorrect, with different explanations. We assume standard modern understanding of haematopoietic stem cell lineages.

Concept / Approach:
In the bone marrow, all blood cells originate from a common multipotent haematopoietic stem cell. This stem cell gives rise to two main progenitor lines: the myeloid stem cell line and the lymphoid stem cell line. The myeloid stem cells produce red blood cells, platelets, granulocytes (neutrophils, eosinophils, basophils) and monocytes, as well as some other cell types. The lymphoid stem cells give rise to lymphocytes, including B cells, T cells and natural killer (NK) cells. Because lymphocytes are leukocytes, and they arise from the lymphoid lineage rather than the myeloid lineage, it is incorrect to say that myeloid stem cells give rise to all leukocytes.

Step-by-Step Solution:
Step 1: List the types of leukocytes: neutrophils, eosinophils, basophils, monocytes and lymphocytes. Step 2: Recall that neutrophils, eosinophils, basophils and monocytes arise from the myeloid stem cell lineage. Step 3: Recall that lymphocytes (B lymphocytes, T lymphocytes and NK cells) arise from the lymphoid stem cell lineage. Step 4: Notice that the statement claims myeloid stem cells give rise to all leukocytes, which would include lymphocytes. Step 5: Since lymphocytes do not arise from myeloid stem cells but from lymphoid stem cells, classify the statement as incorrect and choose the option that explains this accurately.

Verification / Alternative check:
To verify, think about immunology diagrams that show the differentiation tree of blood cells. At the top is a multipotent haematopoietic stem cell, branching into common myeloid progenitor and common lymphoid progenitor. From the myeloid branch come erythrocytes, megakaryocytes (platelets), granulocytes and monocytes. From the lymphoid branch come the different classes of lymphocytes. Since these charts are consistent across textbooks, they confirm that leukocytes arise from both myeloid and lymphoid stem cells, not from the myeloid lineage alone.

Why Other Options Are Wrong:
Option a incorrectly states that all leukocytes come from myeloid stem cells, ignoring the lymphoid lineage. Option c claims the statement is correct only for lymphocytes, which is backwards, because lymphocytes do not come from myeloid stem cells. Option d claims it is correct only for granulocytes but ignores monocytes and misrepresents the original statement, which mentioned all leukocytes. Option e is obviously wrong, because leukocytes do arise from haematopoietic stem cells in the bone marrow. Only option b correctly states that some leukocytes (granulocytes and monocytes) come from myeloid stem cells, while lymphocytes come from lymphoid stem cells.

Common Pitfalls:
A common mistake is to oversimplify haematopoiesis and assume that all white blood cells share a single progenitor lineage, especially if students memorise only the myeloid branch. Another pitfall is to forget that lymphocytes are also leukocytes, leading to confusion about how many stem cell lines are involved. To avoid these errors, visualise the standard haematopoietic tree with two major branches, myeloid and lymphoid, and remember that both produce types of leukocytes. This understanding helps you critically evaluate statements like the one in this question.

Final Answer:
The statement is incorrect: some leukocytes arise from myeloid stem cells, but others arise from lymphoid stem cells.