Hematopoiesis: Lymphoid & Monocytic Series (Lymphocytes & Monocytes)

Vocabulary flashcards covering key concepts from lymphocyte and monocyte development, lymphoid organs, and marker characteristics from the lecture notes.

Lymphocytes

White blood cells that defend the body by recognizing foreign antigens; major groups: T cells, B cells, and NK cells; recirculate between blood and lymphoid tissues.

Plasma cells

Fully differentiated B cells that produce antibodies; mainly in bone marrow; marked by CD138; nucleus eccentrically located with a prominent hof (Golgi apparatus).

Lymphocyte recirculation

Movement of lymphocytes between blood and lymphoid tissues to encounter blood-borne antigens and disseminate memory cells.

Lymphoid progenitor stem cell

Stem cell that gives rise to lymphocytes; precursor to the lymphoid lineage.

Natural killer (NK) cells

Innate immune lymphocytes derived from the lymphoid lineage that kill infected or tumor cells directly; do not require prior antigen exposure.

Central / Primary lymphatic organs

Sites of lymphocyte development: bone marrow and thymus.

Peripheral / Secondary lymphatic organs

Sites where mature lymphocytes migrate and respond to antigens: spleen, lymph nodes, tonsils, and MALT (e.g., Peyer’s patches).

Thymus

Primary lymphoid organ in the anterior mediastinum where T lymphocytes develop; larger in children and involutes with age.

B lymphocytes (B cells)

Lymphocytes that develop in bone marrow; give rise to plasma cells and antibodies; include Pro-B, Pre-B, immature B, and mature B stages.

T lymphocytes (T cells)

Lymphocytes that mature in the thymus; include CD4+ helper and CD8+ cytotoxic subsets; activated T cells help B cells or kill target cells.

CD4+ T lymphocytes

Helper T cells that coordinate immune responses; targets of HIV.

CD8+ T lymphocytes

Cytotoxic T cells that kill infected or abnormal cells; important in antiviral defense.

HIV (human immunodeficiency virus)

Virus that targets CD4+ T lymphocytes; progressive depletion leads to immunodeficiency and AIDS.

Pro-B cell

Early stage in B cell development in bone marrow; markers: CD34+, TdT+, CD22+, CD38high, CD45low.

Pre-B cell

B cell development stage following Pro-B; marker profile includes CD34+, TdT+, CD22+, CD19+, CD79a+; CD10high typically seen.

Immature B cell

Antigen-naïve B cell in bone marrow or blood; markers: CD22+, CD38+, CD19+, CD79a+, CD10low, CD45high.

Mature B cell

Circulating, antigen-experienced B cell; markers: CD20+, CD22+, CD38+, CD19+, CD79a+, CD10low, CD45high; expresses surface IgM/IgD.

Plasma cell markers

CD138 is a key surface marker; abundant cytoplasm and hof; synthesizes and secretes antibodies.

Lymphoblast

Earliest morphologically identifiable lymphoid precursor in bone marrow; large (10–22 μm) with high N:C ratio and delicate chromatin.

Prolymphocyte

Lymphoid precursor stage with oval/indented nucleus, high N:C ratio, and condensed chromatin; more mature than lymphoblasts.

Mature lymphocyte

Normal circulating lymphocyte in peripheral blood; ~30–40% of leukocytes; size 7–15 μm, dense nucleus, scant cytoplasm.

Variant / Reactive lymphocyte

Antigenically stimulated lymphocytes seen in viral infections (e.g., mono, CMV); larger size, abundant cytoplasm, irregular nucleus; may resemble blasts.

Monocytes

White blood cells that function as phagocytes and become macrophages in tissues; comprise 2–11% of circulating leukocytes.

Macrophages

Tissue-resident phagocytes derived from monocytes; named by location (e.g., Kupffer cells, alveolar macrophages, microglia).

Monoblast

Early monocytic precursor in the bone marrow; large (12–20 μm) with a pale cytoplasm and fine chromatin.

Promonocyte

Monocytic precursor following the monoblast; indented nucleus and blue cytoplasm with azure granules; no or few granules.

Mature monocyte

Circulating monocyte ready to migrate into tissues; large cells with horseshoe-shaped nucleus and blue-gray cytoplasm.

Monocyte development (GMP)

Derivation from granulocyte–monocyte progenitor; M-CSF drives growth and differentiation along with IL-3.

M-CSF (macrophage colony-stimulating factor)

Cytokine essential for monocyte differentiation into macrophages; supports monocytic lineage development.

Kupffer cells / alveolar macrophages / osteoclasts / microglia / Langerhans cells

Tissue macrophage variants derived from monocytes in liver, lung, bone, brain, skin, etc.

Lymphoid vs myeloid development

Lymphoid cells arise from lymphoid progenitors; myeloid derivatives (granulocytes, monocytes) arise from GMP; differentiation guided by cytokines.

Germinal and primary lymphoid organs (summary)

Primary organs (bone marrow, thymus) enable lymphocyte development; secondary organs (spleen, nodes, tonsils, MALT) enable activation and proliferation.

Peyer’s patches (MALT)

Mucosa-associated lymphoid tissue in the intestines; sites of antigen encounter and lymphocyte activation.

Lymphoid progenitor cytokines (IL-1, IL-6)

Growth factors driving differentiation of pluripotent stem cells toward the lymphoid lineage.

Antigen

A molecule, typically a protein or polysaccharide, that can bind to an antibody or T-cell receptor and initiate an immune response; recognized as foreign by the immune system.

Antibody / Immunoglobulin (Ig)

A Y-shaped protein produced by plasma cells that is used by the immune system to identify and neutralize foreign objects like bacteria and viruses; specific to particular antigens.

Granulocytes

A type of white blood cell characterized by the presence of granules in its cytoplasm; includes neutrophils, eosinophils, and basophils; involved in innate immunity.

Neutrophils

The most abundant type of granulocyte and white blood cell; first responders to bacterial infection and inflammation; powerful phagocytes.

Dendritic cells

Antigen-presenting cells (APCs) with long, branching projections; found in tissues like skin and mucous membranes; crucial for initiating adaptive immune responses by presenting antigens to T cells.

Antigen-presenting cells (APCs)

Immune cells that display fragments of antigens on their surface to T cells, initiating an adaptive immune response; key examples include dendritic cells, macrophages, and B cells.

Phagocytes

Cells that protect the body by ingesting harmful foreign particles, bacteria, and dead or dying cells; includes macrophages, neutrophils, and monocytes.

Innate Immunity

The body's non-specific, immediate defense system against pathogens; includes physical barriers (skin), chemical barriers (acid), and cells like NK cells, phagocytes, and granulocytes.

Eosinophils

A type of granulocyte that plays a role in allergic reactions, asthma, and defense against parasites; characterized by bilobed nucleus and large, red-orange granules.

Basophils

The least common type of granulocyte; involved in allergic and inflammatory responses, releasing histamine and heparin from their large, dark purple granules.