Immuno kill me

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Neutrophils

• 1ST RESPONDERS THAT INGEST BACTERIA AND FUNGI

• Phagocytes and granulocytes

• Ingest and destroy bacteria and fungi using reactive oxygen species and enzymes (e.g. in granules)

• Form pus; major cells in acute inflammation.

• Short-lived, but crucial for initial defense (deficiency leads to recurrent bacterial/fungal infections)

Eosinophils

• FIGHT HELMINTHS AND TAKE PART IN ALLERGIC RESPONSES

• Phagocytes and Granulocytes

• Attack parasites (especially helminths) too large to phagocytose by releasing toxic granule proteins (e.g., major basic protein) and ROS.

• Involved in allergic responses (eosinophilia seen in allergies)

• Secretes inflammatory mediators and cytokines

Basophils

• MEDIATE IgE-driven reactions

• Phagocytes and granulocytes (LARGEST of the granulocytes)

• Circulating and rare (0.5-1% of WBC), similar function to mast cells

• Important for parasitic infections

• Contains heparin (anticoagulant)

• Bear high-affinity IgE receptors, upon IgE cross-linking (e.g in allergic rxns), release histamine, serotonin, and other mediators, causing inflammation

Mast Cells

• MEDIATE IgE-driven reactions

• Two types (Connective tissue and Mucosal)

• Granulocytes

• Tissue-resident cells (in mucosa, connective tissue) are analogous to basophils

• Trigger acute inflammation and allergic rxns by degranulating (histamine, leukotrienes, prostaglandins) that cause vasodilation, bronchospasm, and increased vascular permeability

• Key effectors in allergies (atopic rxns) and in parasite defense

Monocytes

• PHAGOCYTES AND CYTOKINE SOURCES

• Monocytes (fast): short-lived and rapidly recruited

• Monocytes circulate in the blood and differentiate into macrophages in tissues

• Functions imprinted in the bone marrow

• Homogeneous in the steady state, yet it can arise from distinct precursors.

Macrophages

• PHAGOCYTES AND CYTOKINE SOURCES

• Long-lived phagocytes that engulf and digest microbes and debris

• Act as antigen-presenting cells (APCs) and secrete cytokines (like IL-1, TNF) to orchestrate inflammation. 

• Can be tissue-resident or monocyte-derived (arise from monocytes that invade tissue in response to infection/cancer) 

Dendritic Cells (DCs)

• PROFESSIONAL APCS (antigen-presenting cells) found in tissues; capture antigen (via phagocytosis or pinocytosis) and migrate to lymph nodes to present peptides to T cells. 

• Phagocytes

• Bridge innate and adaptive responses by innate sensing of pathogens and displaying their antigens to T cells of the adaptive system

• Plasmacytoid DCs also produce large amounts of type 1 interferons to antiviral responses.

Natural Killer (NK) Cells 

• KILL STRESSED OR MHC-I LOW CELLS

• Innate lymphocytes that kill virus-infected/tumor cells lacking normal MHC I expression

• Release cytotoxic granules (perforin and granzymes) to induce apoptosis of targets

• Activated by cytokines (IL-12, IFN-a/B) and have inhibitory receptors for MHC I to prevent attacking healthy cells

• Mediate antibody-dependent cellular cytotoxicity (ADCC) via CD16 binding to IgG-coated targets

B Lymphocytes (B Cells)

• MAKE ANTIBODIES AFTER ACTIVATION

• Recognize Antigens via B-cell receptor (membrane Ig)

• After activation → differentiate into plasma cells that secrete antibodies (immunoglobulins)

• Act as APCs (presenting antigen to TH cells) and secrete cytokines

• Originate and mature in bone marrow (primary lymphoid organ)

Plasma Cells

• MAKE ANTIBODIES AFTER ACTIVATION

• Fully differentiated antibody-secreting factories derived from B cells

• Reside in bone marrow or peripheral lymphoid tissues

• Produces large volumes of antibodies specific to the antigen that stimulated the parent B cell

• Extensive Rough ER (for antibody synthesis) and DO NOT typically circulate

• Responsible for humoral immunity (e.g. plasma cells secreting IgA in mucosa, IgG in serum, etc.)

T Cells

• CD4 HELPER AND CD8 CYTOTOXIC ROLES

• Develop in the thymus and orchestrate cell-mediated immunity

• Each T cell has a unique T-cell receptor (TCR) recognizing peptide antigens presented on MHC

Helper T (CD4+) cells

• Provide help via costimulation and cytokines to activate B cells, macrophages, and cytotoxic T cells,

• Organize immune responses

Cytotoxic T (CD8+) cells

• Directly kill infected or cancerous cells by releasing perforin/granzymes (requires antigen presentation on MHC I)

Regulatory T cells (CD4 + CD25 + FoxP3+)

• Suppress immune responses to maintain self-tolerance and prevent autoimmunity

M cells (Microfold Cells) - Mucosal Immunity Cell Type

• Antigen transcytosis; delivery of antigens by endocytosis to lamina propria, Peyer’s patches

• Initiation of adaptive immunity by delivering to DENDRITIC CELLS

Goblet Cells - Mucosal Immunity Cell type