immuno 2: cells

What cells are involved in the immune response and what do they have in common?

Macrophages, dendritic cells, granulocytes, B cells, T cells, and NK cells all arise from hematopoietic stem cells in the bone marrow.

What is hematopoiesis?

Lifelong production of blood and immune cells in bone marrow that generates myeloid and lymphoid lineages.

What are the two major immune cell lineages?

Myeloid (e.g., macrophages, granulocytes) and lymphoid (e.g., B cells, T cells, NK cells).

What are the main functions of macrophages?

Phagocytosis, cytokine secretion for inflammation, and antigen presentation to T cells.

How do macrophages function in innate vs adaptive immunity?

Innate uses PRRs binding PAMP or complement for phagocytosis, while adaptive uses antibodies or complement but performs similar functions overall.

What is opsonization?

Antibodies or complement coat pathogens (opsonins), enhancing their recognition and phagocytosis.

The role of macrophages in innate phagocytosis and secreting cytokines?

Phagocytosis: PRR or oposonization w complement

Secrete cytokines: recruit more cells, inflammation (other functions too)

The role of macrophages in adaptive phagocytosis and secreting cytokines

phagocytosis: opsonization with complement or Abs

secrete cytokines: recruit mroe cells, inflammation (other functions too)

How do macrophages activate T cells?

They process pathogens into peptides and present them on MHC molecules for T cell recognition.

What are neutrophils and their key feature?

The most abundant granulocytes that phagocytose and release toxic substances, often causing collateral tissue damage.

What are the roles of eosinophils, mast cells, and basophils?

Eosinophils fight parasites, while mast cells and basophils mediate allergic and hypersensitivity reactions (mast cells via IgE).

What are dendritic cells and where are they found?

Star-shaped antigen-presenting cells found in tissues like skin, lungs, and GI tract.

What is unique about dendritic cells in immune activation?

They capture antigen in tissues and migrate to secondary lymphoid organs to activate T cells.

What are the major functions of B cells?

Phagocytosis, antigen presentation, antibody production, and formation of memory B cells.

What are plasma cells and memory B cells?

Plasma cells secrete antibodies, while memory B cells provide faster responses upon re-exposure.

What is the BCR and how does it change with activation?

A membrane-bound antibody specific to one antigen; naïve cells have IgM/IgD, activated cells express one isotype (IgG, IgA, IgE, or IgM).

How are T cells activated?

TCRs recognize antigen peptides presented on MHC molecules, not whole antigens.

How do BCRs and TCRs differ?

BCRs bind whole antigen directly, while TCRs require processed antigen presented on MHC.

What are the two main T cell types and their roles?

CD4+ helper T cells coordinate immune responses, while CD8+ cytotoxic T cells kill infected cells.

What MHC do CD4 and CD8 T cells recognize?

CD4 → MHC II, CD8 → MHC I (“always match 8 with I”).

How do CD8+ T cells kill infected cells?

They release lytic enzymes and induce apoptosis in infected cells.

What happens after T cell activation?

They clonally expand and differentiate into effector subsets based on cytokine signals.

What are the main CD4+ T helper subsets?

TH1, TH2, TH17, and Tfh, each defined by cytokine production and immune function.

What are the functions of TH1 and TH2 cells?v

TH1 (IFN-γ) activates macrophages for intracellular pathogens; TH2 (IL-4,5,13) drives allergy and helminth responses.

What do TH17 and Tfh cells do?v

TH17 promotes inflammation and recruits neutrophils for extracellular pathogens, while Tfh supports antibody production and isotype switching.

What are NK cells and how are they different from B/T cells?

Lymphoid cells that kill abnormal cells without antigen-specific receptors.

How do NK cells recognize and kill target cells?

They kill antibody-coated cells (ADCC), cells lacking MHC I, or stressed cells expressing MIC-A/B via NKG2D.

What are the two types of lymphoid organs?

Primary (development) and secondary (activation).

What happens in primary lymphoid organs?

Bone marrow produces cells and develops B cells, while the thymus matures T cells.

What happens in secondary lymphoid organs?

Naïve B and T cells encounter antigen, become activated, and differentiate (e.g., lymph nodes, spleen).