H3N2 influenza virions –CDC PHIL
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There’s a popular belief that once you’ve had a particular strain of the flu, your body’s immune system will protect you against it in the future. And under the right circumstances, that’s true.
But human physiology and its immune response is rarely as simple, and straightforward, as that.
Our immune systems vary considerably from one person to the next, and within a single individual, can change radically over time. We’ve also discovered that some flu viruses leave a stronger `imprint’ on our immune system, than others.
Both of these factors can influence how strong . . . and how long lasting . . . any acquired immunity to a flu virus might be.
Which is one of the reasons why the CDC reminds us to get a flu shot every year, since the immunity from last year’s vaccine (or a bout with the flu) may have diminished over time – even if the same flu strains remain in circulation.
Now a study, published today in Journal of Leukocyte Biology, looks at another variable in influenza infection that appears to influence the type, and strength, of the immune response (at least in mice).
The initial viral dose. The study is called:
Initial infectious dose dictates the innate, adaptive, and memory responses to influenza in the respiratory tract
Isabelle Marois, Alexandre Cloutier, Émilie Garneau and Martin V. Richter
Abstract
Factors from the virus and the host contribute to influenza virus pathogenicity and to the development of immunity. This study thoroughly examined the effects of an initial infectious dose of virus and unveiled new findings concerning the antiviral and inflammatory responses, innate and adaptive immunity, memory responses, and protection against secondary heterologous infection.
In this experiment, researchers infected two groups of mice – one with a low dose and one with a high dose –of influenza A (H3N2), and then gauged various aspects of their immune response. Later, they exposed these mice to a different strain of flu to see what, if any, immune response was `left over’ from the initial infection.
As I’ve cautioned before, mouse models are often very useful in laboratory research, but what happens with mice doesn’t always correspond to what happens with human physiology.
Still, they came up with some intriguing results. They found that the larger the initial infectious dose, the greater, broader, and longer-lived was the immune response.
The full study is behind a pay wall, but we’ve got a press release (slightly reparagraphed for readability) from the Federation of American Societies for Experimental Biology that provides the broad strokes to this research.
Flu immunity is affected by how many viruses actually cause the infection
New research published in the Journal of Leukocyte Biology suggests that the immune response differs depending on the amount of virus received during infection
Bethesda, MD—Not only does the type of flu virus affect a patient's outcome, but a new research report appearing in the Journal of Leukocyte Biology suggests that the number of viruses involved in the initial infection may be important too.
Scientists from Canada found that when mice were infected by relatively high concentrations of the flu virus, they not only developed immunity against the virus that infected them, but this also promoted the generation of a type of immune cell in the lungs poised to rapidly react against infections with other strains of the flu, as well.
Mice that were infected with a relatively low concentration of the virus developed weaker immunity against the strain that infected them, did not build up this crucial population of immune cells in the lungs, and showed only delayed immunity toward other flu strains.
This discovery could pave the way for new prophylactic strategies to fight flu infections and provides a novel basis for vaccine design.
"Hopefully, the findings of our study will help to develop better vaccine preparations that will be more effective in inducing protective cellular immunity to fight against infectious pathogens such as bacteria, viruses and fungi," said Martin V. Richter, Ph.D., the lead researcher involved in the work from the Department of Medicine at the Université de Sherbrooke and Centre de Recherche Clinique Étienne-Le Bel in Québec, Canada.
While both are complex and multifaceted, our immune systems can be divided into two types of protection.
We have natural immunity – so called `innate immunity’ – that can detect, and launch a generic defense against a wide variety of invading pathogens
Were it not for this built-in immunity, none of us would survive past the first few hours or days of life; we'd be quickly overrun by opportunistic infections.
Innate immune system buys us time for our Adaptive Immune System to learn to recognize and fight specific pathogens.
The adaptive immune system produces pathogen-specific antibodies that can remember previous encounters with a virus, and provides us with varying degrees of acquired immunity.
For more information on some of the complexities of our immune system, you may wish to revisit some of these earlier blog posts.
Study: Vitamin D And The Innate Immune System
GM-CSF: An Innate Ability To Fight Flu
Cytokine Storm Warnings
PAMP and Circumstance
And for a fascinating look at the pathogenesis of influenza, the innate immune system, and the role of cytokines I would invite you to read my 3-part look at the Baskin pathogenesis study from 2009.
Dissecting the Influenza Pathogenesis Study Pt. 1
