antigen processing, chemokines, and cytokines

What are the three major types of professional antigen-presenting cells (APCs)?

Dendritic cells, macrophages, and B cells.

Which APCs can activate naïve T cells?

Only dendritic cells can activate naïve T cells.

What are the main functions of dendritic cells?

Capture, process, and present antigens to T cells to initiate the adaptive immune response.

What are the subpopulations of dendritic cells?

Classical (cDC1, cDC2), plasmacytoid (pDC), Langerhans cells, and follicular dendritic cells (fDC).

What do plasmacytoid DCs secrete in response to viral infection?

Large amounts of type I interferons (IFN-α, IFN-β) and type III interferons (IFN-λ).

Where are follicular dendritic cells found?

In germinal centers of lymphoid organs such as lymph nodes, spleen, and Peyer’s patches.

What two characteristics make mature DCs capable of activating naïve T cells?

1) Expression of peptide-MHC and costimulatory molecules; 2) Expression of DC-SIGN for prolonged T cell contact.

What are the two major pathways of antigen processing and presentation?

MHC Class I (endogenous) and MHC Class II (exogenous) pathways.

What is the main function of the MHC Class I pathway?

Presents endogenous peptides to CD8+ cytotoxic T cells.

What is the main function of the MHC Class II pathway?

Presents exogenous peptides to CD4+ helper T cells.

What are the key molecules involved in MHC Class II processing?

Invariant chain, HLA-DM, HLA-DO, and MARCH-1.

What is the function of HLA-DM?

Catalyzes release of CLIP and binding of antigenic peptides in the MHC II compartment.

What is the function of HLA-DO?

Acts as a negative regulator of HLA-DM.

What is the function of MARCH-1?

Regulates MHC II expression through ubiquitination; expression decreases during DC activation.

What molecules are involved in MHC Class I processing?

Proteasome, TAP (Transporter associated with Antigen Processing), and ERAAP.

What is cross-presentation?

Exogenous antigens presented on MHC I molecules to activate CD8+ T cells.

What is autophagy in antigen presentation?

Endogenous antigens presented on MHC II molecules via the autophagy pathway.

How do immune cells communicate with each other?

By secreted molecules (cytokines, chemokines) or direct cell-cell contact via receptor-ligand pairs.

What are chemokines?

Small signaling proteins that attract and direct leukocyte movement (chemotaxis).

What are the main categories of chemokines?

C, CC, CXC, and CX3C chemokines, based on cysteine arrangement.

What is the function of eotaxin (CCL11)?

Recruits eosinophils during allergic or parasitic inflammation.

What is the role of CCL19 and CCL21?

Guide activated dendritic cells from infection sites to lymph nodes via CCR7.

What are cytokines?

Proteins secreted by immune cells to regulate immune and inflammatory responses.

List characteristics of cytokines.

Short-lived, pleiotropic, redundant, locally/systemically active, and tightly regulated.

What are common stimuli for cytokine production?

Antigens, PAMPs, PRR activation, antibodies, and other cytokines.

What are interleukins?

Cytokines that facilitate communication between leukocytes and immune cells.

What are interferons?

Cytokines produced during viral infections that inhibit viral replication.

Name the three types of interferons.

Type I (IFN-α, IFN-β), Type II (IFN-γ), and Type III (IFN-λ).

What is TNF-α?

A cytokine produced by macrophages and T cells that mediates inflammation and apoptosis.

What are the three modes of cytokine action?

Autocrine, paracrine, and endocrine effects.

List the five effects of cytokines on target cells.

Pleiotropy, redundancy, synergy, antagonism, and cascade activation.

How are cytokine functions regulated?

Through receptor expression, antagonists, soluble receptors, SOCS proteins, and tissue binding.

What are the main receptor categories for cytokines?

Channel-linked, tyrosine kinase, G-protein coupled, and sphingomyelinase-activating receptors.

What is the NF-κB pathway?

A pathway activated by TLRs and PAMPs leading to expression of proinflammatory cytokines.

What is the NF-AT pathway?

A calcium-dependent pathway regulating cytokine gene transcription in T cells.

What is the JAK-STAT pathway?

A cytokine signaling pathway where JAKs phosphorylate STATs, leading to gene transcription.