PSC 6130 – Immunology: Overview of the Immune System

These flashcards cover key terms, concepts, cell types, and mechanisms discussed in the PSC 6130 Immunology lecture on the overview of the immune system.

What is the most important physiologic function of the immune system?

To prevent or eradicate infections.

Which branch of immunity is always present and provides the early line of defense against microbes?

Innate immunity

Which branch of immunity requires clonal expansion and differentiation of lymphocytes before it becomes effective?

Adaptive immunity.

What are the two major arms of adaptive immunity and what do they target?

Humoral immunity (antibodies neutralize extracellular microbes/toxins) and cell-mediated immunity (T lymphocytes eradicate intracellular microbes).

What is an antigen?

Any molecule capable of being recognized by an antibody or a T-cell receptor.

What is an immunogen?

A substance that elicits an immune response (all immunogens are antigens, but not all antigens are immunogens).

Define clonal selection.

Activation by antigen of a lymphocyte bearing a complementary receptor, followed by proliferation to form an expanded clone of identical cells.

Define a clone in immunology.

A population of identical cells derived from a single progenitor and sharing the same antigen specificity.

Name three main ways the immune system can go wrong.

Hypersensitivity, immunodeficiency, and autoimmunity.

What immune reaction is the major barrier to successful organ transplantation?

Graft rejection (and related blood transfusion reactions).

List three key differences between innate and adaptive immunity.

Innate is immediate, lacks memory, and uses pattern-recognition receptors; adaptive is delayed (3–5 days), forms memory, and uses highly specific BCR/TCR receptors.

Which receptors on innate immune cells recognize pathogen-associated molecular patterns (PAMPs)?

Pattern recognition receptors (PRRs).

Which cells are the first to encounter pathogens and constitute 50–60% of circulating leukocytes?

Neutrophils.

Which innate cells bridge innate and adaptive immunity by presenting antigens to naïve T cells?

Dendritic cells (macrophages can also present antigens, but dendritic cells are the primary bridge).

Which innate cells release histamine, leukotrienes, and heparin, playing major roles in allergy and parasitic infection?

Eosinophils and basophils (mast cells in tissue perform a similar role).

Which innate lymphocyte is crucial for killing virus-infected or transformed (tumor) cells?

Natural killer (NK) cells.

From what progenitor do myeloid lineage cells arise?

Hematopoietic stem cells in the bone marrow.

What do circulating monocytes become when they migrate into tissues?

Macrophages.

Which cytokines are commonly secreted by activated macrophages?

IL-1β, TNF-α, IL-6, IL-10, IL-12, and IFN-α/β.

What are the antibody-secreting effector cells of the B-lymphocyte lineage?

Plasma cells.

Which T-cell subset expresses CD4 and assists B cells and phagocytes?

Helper T cells (CD4⁺).

Which T-cell subset expresses CD8 and directly kills infected host cells?

Cytotoxic T lymphocytes (CTLs).

Which immunoglobulin is produced first during a primary immune response?

IgM.

What is isotype switching?

A process by which a B cell changes the antibody class it produces (e.g., from IgM to IgG) while retaining antigen specificity.

Which immunoglobulin predominates in mucosal secretions and provides mucosal immunity?

IgA.

Which immunoglobulin binds mast cells and basophils, mediating allergic reactions?

IgE.

Which immunoglobulin is the most abundant in blood and provides long-term systemic protection?

IgG.

What cellular feature allows adaptive immunity to respond faster and stronger upon re-exposure to an antigen?

The presence of antigen-specific memory B and T cells.

What is the primary function of Th1 helper T cells?

Activation of macrophages and assistance in B-cell activation.

How long after infection does the adaptive immune response usually become effective?

Approximately 3–5 days (72–96 hours).

What are pathogen-associated molecular patterns (PAMPs)?

Molecular motifs shared by groups of microbes that are recognized by innate immune receptors.

Which immune system reacts in essentially the same way to repeated infections and recognizes shared microbial structures?

Innate immunity.

What type of immunity is mediated by antibodies produced following B-cell activation?

Humoral immunity.

Which cells are primarily responsible for cell-mediated immunity?

T lymphocytes.

What is the most important physiologic function of the immune system?

To prevent or eradicate infections.

Which branch of immunity is always present and provides the early line of defense against microbes?

Innate immunity.

Which branch of immunity requires clonal expansion and differentiation of lymphocytes before it becomes effective?

Adaptive immunity.

What are the two major arms of adaptive immunity and what do they target?

Humoral immunity (antibodies neutralize extracellular microbes/toxins) and cell-mediated immunity (T lymphocytes eradicate intracellular microbes).

What is an antigen?

Any molecule capable of being recognized by an antibody or a T-cell receptor.

What is an immunogen?

A substance that elicits an immune response (all immunogens are antigens, but not all antigens are immunogens).

Define clonal selection.

Activation by antigen of a lymphocyte bearing a complementary receptor, followed by proliferation to form an expanded clone of identical cells.

Define a clone in immunology.

A population of identical cells derived from a single progenitor and sharing the same antigen specificity.

Name three main ways the immune system can go wrong.

Hypersensitivity, immunodeficiency, and autoimmunity.

What immune reaction is the major barrier to successful organ transplantation?

Graft rejection (and related blood transfusion reactions).

List three key differences between innate and adaptive immunity.

Innate is immediate, lacks memory, and uses pattern-recognition receptors; adaptive is delayed (3–5 days), forms memory, and uses highly specific BCR/TCR receptors.

Which receptors on innate immune cells recognize pathogen-associated molecular patterns (PAMPs)?

Pattern recognition receptors (PRRs).

Which cells are the first to encounter pathogens and constitute 50–60\% of circulating leukocytes?

Neutrophils.

Which innate cells bridge innate and adaptive immunity by presenting antigens to naïve T cells?

Dendritic cells (macrophages can also present antigens, but dendritic cells are the primary bridge).

Which innate cells release histamine, leukotrienes, and heparin, playing major roles in allergy and parasitic infection?

Eosinophils and basophils (mast cells in tissue perform a similar role).

Which innate lymphocyte is crucial for killing virus-infected or transformed (tumor) cells?

Natural killer (NK) cells.

From what progenitor do myeloid lineage cells arise?

Hematopoietic stem cells in the bone marrow.

What do circulating monocytes become when they migrate into tissues?

Macrophages.

Which cytokines are commonly secreted by activated macrophages?

IL-1β, TNF-α, IL-6, IL-10, IL-12, and IFN-α/β.

What are the antibody-secreting effector cells of the B-lymphocyte lineage?

Plasma cells.

Which T-cell subset expresses CD4 and assists B cells and phagocytes?

Helper T cells (CD4⁺).

Which T-cell subset expresses CD8 and directly kills infected host cells?

Cytotoxic T lymphocytes (CTLs).

Which immunoglobulin is produced first during a primary immune response?

IgM.

What is isotype switching?

A process by which a B cell changes the antibody class it produces (e.g., from IgM to IgG) while retaining antigen specificity.

Which immunoglobulin predominates in mucosal secretions and provides mucosal immunity?

IgA.

Which immunoglobulin binds mast cells and basophils, mediating allergic reactions?

IgE.

Which immunoglobulin is the most abundant in blood and provides long-term systemic protection?

IgG.

What cellular feature allows adaptive immunity to respond faster and stronger upon re-exposure to an antigen?

The presence of antigen-specific memory B and T cells.

What is the primary function of Th1 helper T cells?

Activation of macrophages and assistance in B-cell activation.

How long after infection does the adaptive immune response usually become effective?

Approximately 3–5 days (72–96 hours).

What are pathogen-associated molecular patterns (PAMPs)?

Molecular motifs shared by groups of microbes that are recognized by innate immune receptors.

Which immune system reacts in essentially the same way to repeated infections and recognizes shared microbial structures?

Innate immunity.

What type of immunity is mediated by antibodies produced following B-cell activation?

Humoral immunity.

Which cells are primarily responsible for cell-mediated immunity?

T lymphocytes.

What is the primary function of MHC (Major Histocompatibility Complex) molecules?

To present peptide antigens to T lymphocytes.

By what two main mechanisms do Cytotoxic T lymphocytes (CTLs) induce cell death in target cells?

Release of preformed perforin and granzymes that induce apoptosis, and activation of Fas/FasL pathway (death receptors).

Define affinity maturation in the context of humoral immunity.

The process by which B cells produce antibodies with increasing affinity for an antigen during a prolonged or repeated immune response.

What genetic mechanism accounts for the vast diversity of T-cell receptors (TCRs) and B-cell receptors (BCRs)?

Somatic V(D)J recombination.

Which cytokine is critical for the differentiation of naive CD4+ T cells into Th1 helper T cells?

IL-12 (interleukin-12).