Department of Energy Argonne National Laboratory Office of Science NEWTON's Homepage NEWTON's Homepage
NEWTON, Ask A Scientist!
NEWTON Home Page NEWTON Teachers Visit Our Archives Ask A Question How To Ask A Question Question of the Week Our Expert Scientists Volunteer at NEWTON! Frequently Asked Questions Referencing NEWTON About NEWTON About Ask A Scientist Education At Argonne Pathogen Progress

Name: Jj
Status: student
Grade: 9-12
Location: Outside U.S.
Country: USA
Date: Spring 2013

When you get sick what keeps pathogens from multiplying and growing untill they take over your whole body since your immune system takes so long to respond?

The immune system is actually an amazingly versatile system, and responds much faster than you might think.

While it's true that specific adaptive and cell-mediated immune responses against a pathogen can take days to weeks to develop, innate non-specific immune responses begin to respond immediately. For example, an infected cell has lines of defense capable of recognizing invaders using mechanisms such as detection of double-stranded RNA in the cytoplasm or molecules present in the cell walls of bacteria. Recognition of foreign invading particles can set off signaling pathways within the cell that shut down functions the pathogen needs to survive and reproduce, and can even set off pathways leading to programmed cell death, or apoptosis, to keep the pathogen from spreading. At the same time, signals are sent into the extracellular matrix surrounding the infected cell, warning nearby cells of the invading pathogen and creating an environment hostile to infection.

In the case of a pathogen that exists outside of the cells- for example, bacteria invading a wound site- other nonspecific mechanisms come into play. In this case, the scavenger cells of the immune system (including macrophages and dendritic cells) are present in tissues and epithelial layers of skin, and constantly take in particles (phagocytosis). If these cells recognize pathogens, they release signaling molecules that recruit other cells to the area. The mediators released by these cell types induce many non-specific responses, including increasing permeability of blood vessels, thereby allowing more immune cells to reach the affected area, and setting off cascades capable of killing pathogens, such as the complement pathway or cytokine productions, resulting in localized areas of inflammation.

These events take place very quickly, and are a first line of defense against invading pathogens. They also contribute to the development of pathogen-specific adaptive and cell-mediated immunity by ensuring that B and T cells are exposed to pathogens, thereby marshaling both immediate and long-term immune responses.


Nothing, in principle. Different microbes have adapted to a relationship with humans in different ways over time. Some organisms have adapted to be less virulent and make you less sick-the better to keep you alive and a home for them. They may be less transmissible and are happy to "stay put". Others have adapted to making you very sick, very quickly and able stay ahead of your immune system and are easily transmissible so that when you die, they can still find a new host. Some are very virulent in the beginning of a relationship with humans, and get less virulent over long periods of time.

So, while it does take your immune system time to mount a defense, depending on the organism, you could die quickly or survive long enough to beat the disease.


ou have a fundamental error, and that is, that the body’s immune system takes a long time to respond. Not all pathogens multiply exponentially. Some pathogens can lay dormant for years. A classic case is the disease called “shingles”. It is a nerve disorder that affects people who have had chickenpox. This virus can lay dormant for decades, only to appear suddenly, causing pain and itching of the skin and underlying nerves. What triggers this immune disorder, to my knowledge, is not known. In other disorders, the immune system not only responds quickly, but over reacts. One of many examples is the immune systems response to “poison ivy”, and in some people, to fish and/or shell fish. Another response is to the toxic substance, ricin, that is a component of the seeds of the castor oil plant.

Your question is a good one, but the answer is far more complicated than your question.

Vince Calder

Hi Jj,

Thanks for the question. It is your immune system which detects pathogens and responds by actively trying to capture the pathogen. The immune response of fever and inflammation also helps to control pathogen growth.

I hope this helps. Please let me know if you have more questions. Thanks Jef

Click here to return to the Molecular Biology Archives

NEWTON is an electronic community for Science, Math, and Computer Science K-12 Educators, sponsored and operated by Argonne National Laboratory's Educational Programs, Andrew Skipor, Ph.D., Head of Educational Programs.

For assistance with NEWTON contact a System Operator (, or at Argonne's Educational Programs

Educational Programs
Building 223
9700 S. Cass Ave.
Argonne, Illinois
60439-4845, USA
Update: November 2011
Weclome To Newton

Argonne National Laboratory