Explain why each of the following statements is false.
a. There are no mature T cells in the bone marrow.
b. The pluripotent stem cell is one of the most abundant cell types in the bone marrow.
c. There are no stem cells in blood.
d. Activation of macrophages increases their expression of class I MHC molecules, allowing them to present antigen to TH cells more effectively.
e. Mature B cells are closely associated with osteoblasts in the bone marrow.
f. Lymphoid follicles are present only in the spleen and lymph nodes.
g. The FRC guides B cells to follicles.
h. Infection has no influence on the rate of hematopoiesis.
i. Follicular dendritic cells can process and present antigen to T lymphocytes.
j. Dendritic cells arise only from the myeloid lineage.
k. All lymphoid cells have antigen-specific receptors on their membrane.
l. All vertebrates generate B lymphocytes in bone marrow.
m. All vertebrates have a thymus.
n. Jawless vertebrates do not have lymphocytes.
The correct answer and explanation is :
Explanation of Why Each Statement is False
a. There are no mature T cells in the bone marrow.
False: While the bone marrow is the site of T cell progenitor production, mature T cells do circulate in the blood and may be found in low numbers in the bone marrow.
b. The pluripotent stem cell is one of the most abundant cell types in the bone marrow.
False: Hematopoietic stem cells (HSCs) are relatively rare, making up only about 0.01%-0.1% of total bone marrow cells.
c. There are no stem cells in blood.
False: Hematopoietic stem cells (HSCs) can be found in peripheral blood, especially after mobilization via certain treatments or in umbilical cord blood.
d. Activation of macrophages increases their expression of class I MHC molecules, allowing them to present antigen to TH cells more effectively.
False: TH cells (CD4+) recognize antigen presented by MHC class II, not class I, which is primarily involved in CD8+ cytotoxic T cell activation.
e. Mature B cells are closely associated with osteoblasts in the bone marrow.
False: While early B cell development occurs near osteoblasts, mature B cells migrate to secondary lymphoid organs.
f. Lymphoid follicles are present only in the spleen and lymph nodes.
False: Lymphoid follicles also exist in mucosa-associated lymphoid tissues (MALT), such as Peyer’s patches in the gut.
g. The FRC guides B cells to follicles.
False: Follicular dendritic cells (FDCs), not fibroblastic reticular cells (FRCs), guide B cells to follicles.
h. Infection has no influence on the rate of hematopoiesis.
False: Infections trigger increased hematopoiesis to produce immune cells like neutrophils and lymphocytes.
i. Follicular dendritic cells can process and present antigen to T lymphocytes.
False: FDCs present antigens to B cells, not T cells, and do so without MHC molecules.
j. Dendritic cells arise only from the myeloid lineage.
False: While most dendritic cells come from the myeloid lineage, plasmacytoid dendritic cells arise from the lymphoid lineage.
k. All lymphoid cells have antigen-specific receptors on their membrane.
False: Natural killer (NK) cells are lymphoid but lack antigen-specific receptors.
l. All vertebrates generate B lymphocytes in bone marrow.
False: In birds, B cells develop in the bursa of Fabricius, not the bone marrow.
m. All vertebrates have a thymus.
False: Some primitive vertebrates, like certain fish, lack a true thymus but may have alternative lymphoid structures.
n. Jawless vertebrates do not have lymphocytes.
False: Jawless vertebrates (e.g., lampreys) lack conventional adaptive immunity but have lymphocyte-like cells using variable lymphocyte receptors (VLRs) instead of immunoglobulins.