# CD40

> English word · Noun

## Definitions
1. a costimulatory protein found on antigen presenting cells and required for their activation by CD154 of T_H cells, with deficiency of CD40 possibly leading to hyper-IgM syndrome type 3.

## Etymology
from cluster of differentiation

## Source
Compiled from Wiktionary via kaikki.org (CC BY-SA). Data vintage: 2026-05-06.
Canonical page: https://plainspell.com/en/word/cd40