The mucosal immune system is that portion of the immune system

Immune system

An immune system is a system of biological structures and processes within an organism that protects against disease by identifying and killing pathogens and tumor cells. It detects a wide variety of agents, from viruses to parasitic worms, and needs to distinguish them from the organism's own...

 which provides protection to an organism

Organism

In biology, an organism is any contiguous living system . In at least some form, all organisms are capable of response to stimuli, reproduction, growth and development, and maintenance of homoeostasis as a stable whole.An organism may either be unicellular or, as in the case of humans, comprise...

's various mucous membrane

Mucous membrane

The mucous membranes are linings of mostly endodermal origin, covered in epithelium, which are involved in absorption and secretion. They line cavities that are exposed to the external environment and internal organs...

s from invasion by potentially pathogenic microbes. It provides three main functions: protecting the mucus membrane against infection, preventing the uptake of antigens, microorganisms, and other foreign materials, and moderating the organism's immune response to that material.

At birth, the neonate

Infant

A newborn or baby is the very young offspring of a human or other mammal. A newborn is an infant who is within hours, days, or up to a few weeks from birth. In medical contexts, newborn or neonate refers to an infant in the first 28 days after birth...

's mucosal immune system is relatively undeveloped, but the colonization of intestinal flora accelerates its development.

Because of its front-line status within the immune system, the mucosal immune system is being investigated for use in vaccines for various afflictions, including AIDS

AIDS

Acquired immune deficiency syndrome or acquired immunodeficiency syndrome is a disease of the human immune system caused by the human immunodeficiency virus...

 and allergies.