# Cytokines and Interleukins Overview

> Cytokines and interleukins for NEET-PG Microbiology, covering IL-1, IL-2, IL-4, IL-12, IL-17, interferons and TNF-α with sources and functions.

- Canonical URL: https://prepelephant.com/topics/neet-pg/microbiology/cytokines-and-interleukins-overview
- Exam / course: NEET-PG · Subject: Microbiology
- Publisher: PrepElephant (https://prepelephant.com) — Prepared and reviewed by the PrepElephant Academic Review Team
- First published: 2026-10-14
- Last updated: 2026-10-14
- Reference basis: Abbas, Lichtman and Pillai Cellular and Molecular Immunology; Janeway's Immunobiology; Ananthanarayan and Paniker's Textbook of Microbiology
- How to cite: "Cytokines and Interleukins Overview", PrepElephant, https://prepelephant.com/topics/neet-pg/microbiology/cytokines-and-interleukins-overview

## Direct answer

Interleukins are a large family of cytokines, secreted proteins that let leukocytes signal one another during innate and adaptive immune responses. Key examples include IL-1 and TNF-α for inflammation, IL-12 and IFN-γ for Th1 immunity, IL-4 for Th2 responses and IL-2 for T cell proliferation. Each cytokine has a characteristic cellular source and a dominant biological effect, and examiners test both.

## What you must remember

- **IL-1 and TNF-α:** the early inflammatory pair from macrophages, producing fever, endothelial activation and acute phase changes, with TNF-α central to septic shock.
- **IL-2:** the T cell growth factor secreted by activated T cells, driving clonal expansion and supporting regulatory T cell survival.
- **IL-4, IL-5 and IL-13:** Th2 cytokines that drive IgE switching, eosinophil activation and mucus secretion, central to allergy and helminth defence.
- **IL-12 and IFN-γ:** the Th1 axis, in which IL-12 from dendritic cells drives IFN-γ production that activates macrophages against intracellular pathogens.
- **IL-17:** the Th17 cytokine that recruits neutrophils and drives antimicrobial responses at mucosal surfaces.
- **Type I interferons:** IFN-α and IFN-β, made by virus-infected cells, which induce an antiviral state in neighbouring cells.
- **IL-10 and TGF-β:** inhibitory cytokines that dampen Th1 and macrophage responses and underpin regulatory T cell function.

## Matching each cytokine to its source and effect

Cytokines are easiest to remember as a grid of source and effect, because most exam questions give one and ask for the other. The table lists the cytokines most often tested in NEET-PG Microbiology.

| Cytokine | Main source | Key function |
|---|---|---|
| IL-1 | Macrophages | Fever, endogenous pyrogen, local inflammation |
| IL-2 | Activated T cells | T cell growth and proliferation |
| IL-4 | Th2 cells | IgE switching, Th2 differentiation |
| IL-6 | Macrophages, T cells, endothelium | Acute phase response, fever, B cell differentiation |
| IL-10 | Th2 cells, regulatory T cells, macrophages | Anti-inflammatory, suppresses Th1 responses |
| IL-12 | Dendritic cells, macrophages | Drives Th1 differentiation and IFN-γ production |
| IFN-γ | Th1 cells, NK cells | Activates macrophages, raises MHC class II expression |
| TNF-α | Macrophages | Fever, septic shock, granuloma formation, cachexia |

The inflammatory cytokines IL-1, IL-6 and TNF-α share a common macrophage origin and an acute phase effect. IL-12 and IFN-γ work as a pair for cell-mediated defence, while IL-4 and IL-10 sit on the opposing humoral and inhibitory side.

## Where the exam tries to catch you

Cytokine questions often mix up a source with a function, so checking both halves of each pairing prevents most errors.

- **Trap:** attributing fever to IL-2 — **Correct:** IL-1, IL-6 and TNF-α are the pyrogenic cytokines, whereas IL-2 is the T cell growth factor.
- **Trap:** listing IFN-γ as a type I interferon — **Correct:** IFN-γ is a type II interferon from T and NK cells, whereas IFN-α and IFN-β are type I and antiviral.
- **Trap:** linking IL-4 with cell-mediated immunity — **Correct:** IL-4 drives humoral Th2 responses and IgE switching, whereas IL-12 and IFN-γ drive cell-mediated Th1 immunity.

## Frequently asked questions

### Which cytokine is the classic endogenous pyrogen?
Interleukin-1 is the classic endogenous pyrogen, released mainly by macrophages and acting on the hypothalamus to raise body temperature. Interleukin-6 and TNF-α also contribute to fever, which is why the three are grouped together as pyrogenic cytokines.

### Which interleukin is known as the T cell growth factor?
Interleukin-2 is known as the T cell growth factor because activated T cells secrete it to drive their own proliferation. Its receptor, CD25, is also present on regulatory T cells, which depend on IL-2 for survival and suppressive function.

### Which cytokines drive the Th2 response in allergy?
IL-4, IL-5 and IL-13 drive the Th2 response in allergy. IL-4 promotes IgE class switching, IL-5 supports eosinophil production and activation, and IL-13 contributes to airway mucus secretion and bronchial hyper-responsiveness.

### What is the difference between type I and type II interferons?
Type I interferons include IFN-α and IFN-β, which are secreted by virus-infected cells and induce an antiviral state in neighbouring cells. The only type II interferon is IFN-γ, which is secreted by Th1 and NK cells and mainly activates macrophages.