Neuroimmunology and Immune-Brain Interactions

Vocabulary flashcards reviewing peripheral and central immune system components, microglial states, fractalkine signaling, neuro-immune pathways, blood-brain barrier mechanisms, and the gut-immune-brain axis.

Innate Immune System

The non-specific defense system against pathogens that includes cells such as macrophages, dendritic cells, monocytes, neutrophils, and natural killer cells.

Macrophages

Antigen-presenting cells that phagocytose pathogens using intracellular lysosomes, present antigens on cell-surface MHCII molecules to signal T cells, and release cytokines.

Neutrophils

Innate immune cells that cluster at sites of infection via cytokine attraction and undergo apoptosis to release lysosomes.

Natural Killer Cells

Innate lymphocytes that exhibit cytotoxicity against viral-infected or tumor cells by boring holes in stressed cells using perforins.

CD4+ Helper T Cells

Adaptive immune cells that recognize antigens presented on MHCII molecules, release cytokines, and activate B cells to produce antibodies to coordinate the immune response.

CD8+ Cytotoxic T Cells

Adaptive immune cells that directly kill infected or tumor cells by recognizing antigens presented on MHCI molecules and releasing perforins/enzymes to induce apoptosis.

Regulatory T Cells

T cells that suppress and regulate the immune response, prevent excessive inflammation, reduce autoimmune reactions, and release anti-inflammatory cytokines such as IL-10.

Toll-Like Receptors (TLRs)

Pattern recognition receptors located on immune cells that recognize pathogen-associated molecular patterns (PAMPs), such as LPS, to play a key role in the innate immune response.

Amoeboid State

The activated morphological state of microglia triggered by neuronal injury or pathogen detection, characterized by having fewer branches.

Quiescent State

The non-activated surveillance state of microglia where they maintain a branched morphology, wrap around neurons, nibble at synapses, and continuously monitor brain tissue.

Fractalkine Signaling

A direct neuron-microglia communication pathway involving fractalkine (CX3CL1) produced by neurons and CX3CR1 receptors expressed on microglia.

Tethered Fractalkine

The membrane-bound form of fractalkine that acts as a microglial brake to keep microglia in a surveillance state and prevent overreaction.

Soluble Fractalkine

The cleaved form of fractalkine that acts as an alert signal for neuronal distress or activity, promoting microglial morphological changes, cytokine release, and synaptic remodeling.

IDO Pathway

A metabolic pathway upregulated by inflammatory cytokines (such as \text{IFN-}\text{\textalpha}) that shunts tryptophan breakdown away from serotonin toward kynurenine and quinolinic acid.

Quinolinic Acid

An NMDA receptor agonist produced via the IDO pathway whose elevated levels contribute to neurotoxicity and depression.

Kynurenic Acid

An NMDA receptor antagonist produced in the IDO pathway whose elevated levels are associated with schizophrenia.

Astrocytes

Abundant glial cells in the CNS that support the blood-brain barrier via endfeet, regulate glutamate-glutamine conversion at tripartite synapses, and balance pro-inflammatory responses.

Area Postrema

A circumventricular structure located in the dorsal vagal complex near the 4th ventricle that possesses a weaker blood-brain barrier, allowing sensing of circulating factors in the blood.

JAK/STAT Pathway

A intracellular signaling pathway initiated by cytokine binding that leads to JAK phosphorylation of STAT, STAT dimerization, and nuclear translocation for gene expression.

Vagus Nerve

Cranial nerve X providing bidirectional neuro-immune communication, consisting of sensory afferents to the NTS and parasympathetic efferents from the DMV and NAmb.

Nucleus Ambiguus (NAmb)

A brainstem nucleus sending post-ganglionic parasympathetic motor signals to the heart to regulate heart rate variability (HRV).

Microbiome Dysbiosis

An imbalance in gut microbial communities often triggered by chronic stress, leading to increased intestinal permeability, immune activation, and altered brain signaling.