Institutionen Södersjukhuset / Karolinska Institutet, Stockholm Söder Hospital
Abstract
Human Immunodeficiency Virus (HIV) transmission occurs primarily after
hetero- and homosexual contact and across mucosal surfaces. The immune
response in mucosal tissues is typified by secretory immunoglobulin A
(SIgA), which is the predominant lg class in human external secretions.
Since the dimeric lgA molecule is stabilized by the attendant J-chain and
the secretory component, it has the unique capacity to maintain its
function in an environment rich in proteolytic enzymes (e.g. mucosal
compartments).
This study was designed to investigate the biological function of local
versus systemic humoral response against HIV infection. Furthermore, to
define lgA mediated neutralization against both primary and T cell line
adapted HIV-1 and HIV-2 isolates. The innate local defense in the oral
cavity against HIV transmission was additionally adressed by
investigating the presence and biological function of secretory leukocyte
proteinase inhibitor (SLPI). The locally produced anti-HIV responses were
investigated both with respect to different stages of disease and with
respect to the time of follow-up.
Using synthetic peptides representing earlier identified antigenic sites
of the HIV-1 and HIV-2 proteins for IgG antibodies in serum, we
illustrated potential epitopes for salivary and serum derived lgA
antibodies. lgA mediated response against HIV-1 was found to be mainly
directed against epitopes in the second and fourth variable regions (V2
and V4) of gpl20. In contrast, we found strongest lgA binding activity
against a region (aa 615-658) in the central part of gp36 in HIV-2.
The neutralizing activity mediated by lgA antibodies could not be
correlated to the total amount of lgA in saliva or serum, or to any
dominance in neutralizing activity against primary isolates with a
specific biological phenotype. The high degree of inter-individual
variability in neutralizing capacity indicate that the presence of
functional, specific anti-HIV1 lgA antibodies is not a general phenomenon
and can not be associated with elevated levels of total lgA but can be
observed on an individual basis, even in late stages of disease.
A persistent longitudinal SIgA response was also found in salivary
samples from four out of eleven HIV-1 infected patients during a
follow-up period of three years. These samples contained highly specific
anti-HIV-1 SIgA with neutralizing activity against both a T cell adapted
strain and four primary isolates. Furthermore, serum derived lgA obtained
from two different cohorts, one in Guinea Bissau and one in Portugal
demonstrated neutralizing capacity against HIV-2.
Among several salivary derived innate factors with antiviral effect, SLPI
is the only protein proved to be efficient in physiological
concentrations. We have investigated the biological function of SLPI in
salivary mediated inhibition of HIV infection and in addition the
inhibitory effect of recombinant SLPI on isolates with various virus
tropism. No significant difference in salivary concentrations of SLPI
could be found between HIV infected individuals and healthy controls.
Elevated levels of salivary SLPI could be associated with an increased
inhibitory effect of the whole saliva sample against HIV-1 isolates. The
inhibitory effect was found to decrease with broad co-receptor usage of
the virus. To further elucidate the mechanisms of SLPI in the entry stage
of the lifecycle of HIV1, we used a panel of virus isolates with distinct
molecular phenotype. The monotropic strains, using either CXCR4 or CCR5
were shown to be most receptive to the inhibitory effect of rSLPI, while
multitropic strains displayed a lower sensitivity to the protein