Inmunidad Humoral

The ISME Journal (2008) 2, 728–738
& 2008 International Society for Microbial Ecology All rights reserved 1751-7362/08 $30.00
www.nature.com/ismej

ORIGINAL ARTICLE

Humoral immunity to commensal oral
bacteria in human infants: evidence that
Streptococcus mitis biovar 1 colonization
induces strain-specific salivary
immunoglobulin A antibodies
Katherine A Wirth1, George H Bowden2,Jennifer L Kirchherr1, Dorothy A Richmond3,
Michael J Sheridan4 and Michael F Cole1
1

Department of Microbiology and Immunology, Georgetown University Medical Center, Washington, DC,
USA; 2Department of Oral Biology, University of Manitoba, Winnipeg, Canada; 3Department of Pediatrics,
Georgetown University Medical Center, Washington, DC, USA and 4Department of Medicine, INOVA Fairfax
Hospital,Fairfax, VA, USA

To define the relationship between salivary SIgA antibodies and commensal oral bacteria, we
examined the reactivity of SIgA antibodies from the saliva of four infants with their own colonizing
Streptococcus mitis biovar 1 (S. mitis bv 1) clones (ribotypes). Immunoblot analysis was used to
examine reactivity of these antibodies with persistent ribotypes isolated from themouths of the
infants over the first year postpartum. Results showed that the pattern of SIgA antibody reactivity
with the majority of clones increased in complexity after colonization but that most additional bands
were common to other clones, indicating that they represented shared antigens. However, unique
bands were identified in 75% of the selected persistent clones. We hypothesized that ifstrainspecific SIgA antibody was induced in response to colonization of a particular clone and contributed
to its elimination from the mouth, then the appearance of unique bands would immediately precede
the disappearance of the strain. Seventy-three percent of all unique bands identified in the study
fulfilled this criterion. Because the mouth is an open, dynamic environment and multiplefactors are
believed to play a role in the immune response at mucosal surfaces, it may not be possible to
conclusively define the relationship between SIgA antibody and commensal bacteria. However, our
data provide evidence that SIgA antibody, reactive with unique antigens of their own colonizing
strains, is produced in infants and may point to a role of this antibody in regulating colonization byS. mitis bv 1.
The ISME Journal (2008) 2, 728–738; doi:10.1038/ismej.2008.26; published online 17 April 2008
Subject Category: microbe–microbe and microbe–host interactions
Keywords: S. mitis biovar 1; infants; saliva; SIgA antibody

Introduction
The mucosal surfaces of the adult human comprise
an area in the order of 400 m2 (Mestecky and
McGhee, 1987). These barrier epithelia are, for themost part, delicate monolayers involved in the
exchange of gases, the uptake of nutrients, excretion
of waste products and other essential physiological

Correspondence: MF Cole, Department of Microbiology and
Immunology, Georgetown University Medical Center, Med-Dent
SE308A, 3900 Reservoir Road, NW, Washington, DC 20057, USA.
E-mail: colem@georgetown.edu
Received 14 November 2007;revised 14 February 2008; accepted
15 February 2008; published online 17 April 2008

functions. Such is the potential susceptibility of
these surfaces to colonization and invasion by
microbial pathogens that mammals and birds have
evolved a sophisticated adaptive immune system,
termed the mucosal immune system, to protect these
surfaces. The mucosal immune system consists of
sentinel secondarylymphoid tissue that is present at
the portals of entry to the mucosae and is distributed
throughout the aerodigestive tract, the genitourinary
tract, eyes and mammary glands. Over 80% of the
total number of B cells in humans are located in the
alimentary canal and are committed to the synthesis
of secretory immunoglobulin A (SIgA), the principal
immunoglobulin isotype secreted onto...