The role of interleukin-8 in the immunopathogenesis of HIV-1 disease and tuberculosis
Date
2014-05-27
Authors
Meddows-Taylor, Stephen
Journal Title
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Abstract
Interleukin-8 (IL-8), a member of the C-X-C chemokine subfamily, is an important
chemoattractant and cellular activator. This study was conducted to determine the role of IL-8
in the immunopathogenesis of HIV-I disease and tuberculosis.
The first section involved determining the effect of infection with HIV-1, Mycobacterium
tuberculosis and co-infection with both of these organisms on IL-8 j_ roduction in vivo. This was
monitored by the determination of levels of serum or plasma EL-8 and peripheral cell-associated
IL-8, assessing peripheral mononuclear (PBMC) and polymorphonuclear (PMN) cell capacity to
produce IL-8 spontaneously or in response to various stimuli, and the detection of constitutive
IL-8 mKNA expression in purified subsets of mononuclear cells. Results show that whereas there
is evidence of detectable levels of cell-associated EL-8 (mKNA and protein) in peripheral cells of
healthy individuals, this is largely lost in the disease states studied. Coupled with this was
significantly increased circulating levels of EL-8 in serum and plasma found in HIV-1 infected
individuals with or without concomitant pulmonary TB. On the other hand, the capacity of PBMC
to produce IL-8 spontaneously ex vivo was enhanced in HIV-1 and TB patients and many of the
HFV/TB group, but their corresponding capacities to respond to various stimuli was significantly
diminished when compared to that of the normal donors. The release of IL-8 from PMN in the
presence of an agonist was diminished mainly in individuals with pulmonary TB, which was
further exacerbated by the presence of HIV-1 infection.
HIV-1-infected individuals have an increased incidence of bacterial infections which could
be related to defective functioning of PMN. The second section was aimed at detecting PMN
abnormalities in HIV and I-HV/TB patients by monitoring EL-8-induced p-glucuronidase release
and PMN chemotaxis in response to IL-8. IL-8-induced (I-glucuronidase release from PMN of
normal individuals and TB patients occurred in a dose-dependent manner. In contrast, PMN from
HTV-1 infected individuals, whether co-infected with M tuberculosis or not, showed a reciprocal
response in that increasing IL-8 concentrations resulted in decreased enzyme release. This
reciprocal slope of the IL-8 dose-response curve was altered for the majority of HIV-1 positive
individuals tested irrespective of their CD4+ cell counts. In addition, PMN chemotaxis in response
to IL-8 was also found to be significantly impaired in a group of HIV-1 infected patients coinfected
w ithM tuberculosis when compared to healthy individuals.
The third section of the study involved analysing the expression of the PMN cell surface
markers, FcyRIII (CD 16), and the two human IL-8 receptors, designated IL -8RA and 1L-8RB.
FcyRIII (CD 16) expression on the surface of PMN was significantly reduced in HIV-1
seropositive patients with pulmonary tuberculosis when compared to those individuals with either
disease alone or healthy blood donors. A significant reduction in the percentage of PMN
expressing IL-8RA and IL-8RB and in their respective fluorescence intensities was found in TB,
HIV, and HTV/TB groups when compared to that obtained for the ND group. IL-8RA intensity
of fluorescence was significantly decreased in the HTV/TB group when compared to the TB and
HIV groups indicating a further down-regulation of IL-8RA expression owing to dual infection.
On the other hand, IL-8RB fluorescence intensity was substantially reduced on PMN from
patients with pulmonary TB and to a greater degree in those patients co-infected with HIV-1 and
M. tuberculosis. Having found a reduction in the expression of both IL-8 receptors on PMN in
all the infection groups, cellular events following the binding of IL-8 to IL-8 receptors on PMN
isolated from dually infected patients, the group which showed the greatest reduction in IL-8
expression was analysed. Results indicated that the impairment of DL-8-dependent PMN functions
such as degranulation and chemotaxis was associated with the reduced expression of IL-8
receptors on these cells.
Increased circulating levels of IL-8 in HIV-1 infection and a diminished cellular capacity
to produce IL-8 as shown in this study may have important implications for antimicrobial defences
and normal immune processes. A dysregulated production of IL-8 in vivo is likely to play a role
in the pathogenesis of HIV-1 disease, pulmonary tuberculosis, and dual infections with both
organisms. In addition, cellular responses dependent on specific receptor engagement and the
subsequent translation of signal transducing events that lead to phagocyte effector functions are
clearly impaired in IL-8 receptor deficient phagocytes. Abnormal PMN functioning in HTV-1
infected individuals, as shown here by defective degranulation and chemotactic responses, have
important implications in the pathogenesis of HIV-1 infection in terms of their ability to clear
secondary microbial infections. Future attempts should be aimed at defining the mechanisms that
bring about these changes in order to contribute to a greater understanding of the mechanisms that
lead to an enhanced risk of superinfections in immunosuppressed individuals.