Mother-to-Child HIV-1 Transmission Events Are Differentially Impacted by Breast Milk and Its Components from HIV-1-Infected Women.

Breast milk is a vehicle of infection and source of protection in post-natal mother-to-child HIV-1 transmission (MTCT). Understanding the mechanism by which breast milk limits vertical transmission will provide critical insight into the design of preventive and therapeutic approaches to interrupt HIV-1 mucosal transmission. However, characterization of the inhibitory activity of breast milk in human intestinal mucosa, the portal of entry in postnatal MTCT, has been constrained by the limited availability of primary mucosal target cells and tissues to recapitulate mucosal transmission ex vivo. Here, we characterized the impact of skimmed breast milk, breast milk antibodies (Igs) and non-Ig components from HIV-1-infected Ugandan women on the major events of HIV-1 mucosal transmission using primary human intestinal cells and tissues. HIV-1-specific IgG antibodies and non-Ig components in breast milk inhibited the uptake of Ugandan HIV-1 isolates by primary human intestinal epithelial cells, viral replication in and transport of HIV-1- bearing dendritic cells through the human intestinal mucosa. Breast milk HIV-1-specific IgG and IgA, as well as innate factors, blocked the uptake and transport of HIV-1 through intestinal mucosa. Thus, breast milk components have distinct and complementary effects in reducing HIV-1 uptake, transport through and replication in the intestinal mucosa and, therefore, likely contribute to preventing postnatal HIV-1 transmission. Our data suggests that a successful preventive or therapeutic approach would require multiple immune factors acting at multiple steps in the HIV-1 mucosal transmission process.

Neutralization of HIV subtypes A and D by breast milk IgG from women with HIV infection in Uganda.

OBJECTIVES: Among HIV-exposed infants in resource-limited countries, 8-12% are infected postnatally by breastfeeding. However, most of those uninfected at birth remain uninfected over time despite daily exposure to HIV in breast milk. Thus, we assessed the HIV-inhibitory activity of breast milk. METHODS: We measured cross-clade neutralization in activated PBMC of Ugandan subtype A (92UG031) and D (92UG005) primary HIV by breast milk or purified milk IgG and IgA from 25 HIV-infected Ugandan women. Isotype-specific antigen recognition was resolved by immunoblot. We determined HIV subtype from envelope population sequences in cells from 13 milk samples by PCR. RESULTS: Milk inhibited p24 production by ≥50% (dose-dependent) by subtype A (21/25; 84%) and subtype D (11/25; 44%). IgG consistently reacted with multiple HIV antigens, including gp120/gp41, but IgA primarily recognized p24 alone. Depletion of IgG (n = 5), not IgA, diminished neutralization (mean 78 ± 33%) that was largely restored by IgG repletion. Mothers infected with subtype A more effectively neutralized subtype A than D. CONCLUSIONS: Breast milk from HIV-infected women showed homotypic and cross-subtype neutralization of HIV by IgG-dependent and -independent mechanisms. These data direct further investigations into mechanisms of resistance against postnatal transmission of HIV to infants from their mothers.

Humoral responses to oxidized low-density lipoprotein and related bacterial antigens after pneumococcal vaccine.

Antibodies to oxidized low-density lipoprotein (oxLDL) may modulate the development of atherosclerosis. Antibodies to oxLDL may also react with cell wall polysaccharides (CWPS) of Streptococcus pneumoniae because both antigens share a common phosphorylcholine moiety. In hypercholesteremic mice, immunization with pneumococcal organisms elicited antibodies to oxLDL and protection against atherosclerosis. In humans, we determined whether the widely used adult pneumococcal polysaccharide vaccine augmented antibodies to oxLDL, CWPS, and phosphorylcholine, providing the potential to retard atherogenesis. Before and 4 weeks after pneumococcal vaccination of 23 healthy adults (11 smokers and 12 matched nonsmokers), we characterized IgG, IgM, and IgA to pneumococcal capsular polysaccharides, CWPS, and phosphorylcholine, IgG and IgM to oxLDL, and fasting serum lipids. The pneumococcal vaccine elicited significant increases in each antibody class to surface capsular polysaccharides. In contrast, only IgG to CWPS increased modestly and only among smokers. Moreover, antibodies to neither phosphorylcholine nor oxLDL increased consistently in either group. The pneumococcal polysaccharide vaccine effectively elicits antibodies to the bacterial capsule. The vaccine had no effect on serum lipids. The vaccine did not augment antibodies to CWPS, to its component phosphorylcholine, or to oxLDL, which are antibodies that have been proposed to modify the uptake of oxLDL by macrophages and the pathogenesis of atherosclerosis.

Inhibition of HIV-1 infectivity and epithelial cell transfer by human monoclonal IgG and IgA antibodies carrying the b12 V region.

Both IgG and secretory IgA Abs in mucosal secretions have been implicated in blocking the earliest events in HIV-1 transit across epithelial barriers, although the mechanisms by which this occurs remain largely unknown. In this study, we report the production and characterization of a human rIgA(2) mAb that carries the V regions of IgG1 b12, a potent and broadly neutralizing anti-gp120 Ab which has been shown to protect macaques against vaginal simian/HIV challenge. Monomeric, dimeric, polymeric, and secretory IgA(2) derivatives of b12 reacted with gp120 and neutralized CCR5- and CXCR4-tropic strains of HIV-1 in vitro. With respect to the protective effects of these Abs at mucosal surfaces, we demonstrated that IgG1 b12 and IgA(2) b12 inhibited the transfer of cell-free HIV-1 from ME-180 cells, a human cervical epithelial cell line, as well as Caco-2 cells, a human colonic epithelial cell line, to human PBMCs. Inhibition of viral transfer was due to the ability of b12 to block both viral attachment to and uptake by epithelial cells. These data demonstrate that IgG and IgA MAbs directed against a highly conserved epitope on gp120 can interfere with the earliest steps in HIV-1 transmission across mucosal surfaces, and reveal a possible mechanism by which b12 protects the vaginal mucosal against viral challenge in vivo.