A deficiency in immune response may predispose patients who have atopic dermatitis (eczema) to developing the skin condition eczema vaccinatum after being administered smallpox vaccine, according to a study published in the journal Immunity.

"I believe these findings could have a significant impact on our ability to vaccinate individuals with eczema and better protect them against potential bio-terrorist attacks involving smallpox," said Michael Howell, a co-author of the study and instructor of pediatrics at the Denver-based National Jewish Medical and Research Center, where the research was conducted. "We identify potential therapies, which should be further tested to determine if they can effectively and safely protect susceptible patients against eczema vaccinatum."

In the study, researchers found that lower levels of LL-37 - an antimicrobial peptide - in the skin of patients with atopic dermatitis allowed the vaccinia virus to grow uncontrollably. Skin cells from atopic dermatitis patients failed to increase LL-37 production in response to the vaccinia virus infection, while skin cells from healthy control-subjects stimulated LL-37 production.

Eczema vaccinatum, which kills up to 6 percent of those affected, occurs when the vaccinia virus, which is currently used for the smallpox vaccine, replicates uncontrollably and circulates through the entire body. Up to 30 percent of children younger than 2 years of age with the disease die. It is also possible that atopic dermatitis patients can develop eczema vaccinatum even if they don't get the vaccine, but come into close personal contact with people who recently received the vaccine.

"It is becoming increasingly clear how important antimicrobial peptides are in immune defense," noted Donald Leung, one of the study's researchers. "They are part of the fast-acting, innate immune response. Because atopic dermatitis patients fail to mount a vigorous innate response with antimicrobial peptides, vaccinia virus infection gets well established and the slower adaptive immune response cannot eradicate it."