HIV infection

Breast milk contains maternal antibodies. All basic forms of immunoglobulins IgG, IgM, IgA, IgD, and IgE are present in breast milk. The most abundant is usually secretory IgA (Lawrence, 1994). The role of HIV-specific antibodies in breast milk in inhibiting HIV transmission through breastfeeding has been investigated. Breast milk in women with established HIV infection has been found to have HIV-specific IgG, with its wide spectrum of activity against HIV proteins, comparable to HIV-specific IgG in serum. The spectrum of activity of serum IgA against HIV has been found to be similar to that of serum IgG, but the spectrum of activity of HIV-specific secretory IgA (sIgA) in breast milk is directed against only a limited number of viral proteins (env protein, gp 160, core proteins).

In a study of breast-milk samples from 215 HIV-infected women in Rwanda (Van de Perre et al., 1993), the most frequently identified HIV-specific antibody in breast milk was IgG (in >95% of samples), the next was IgM (in 41-78% of samples) and the least frequent was IgA (in 23-41% of samples). Lack of persistence of HIV-specific IgM in breast milk collected at 18 months was associated with a high risk of transmission of HIV. Of 20 children receiving breast milk with detectable HIV DNA in samples collected at day 15, but without detectable IgM in later samples, 47% were infected with HIV. In those with detectable DNA in breast milk samples at day 15, and with IgM in later samples only 30% became infected. This suggests that IgM may protect against breast-milk transmission of HIV. The rate of transmission was 18% in infants of mothers whose breast-milk sample at day 15 had undetectable HIV DNA, regardless of IgM levels (Van de Perre et al., 1993).

Other components of breast milk are protective against viral infections. Human lactoferrin has been shown in vitro to have an inhibitory activity against HIV (Harmsen et al., 1995), and lipid-dependent antiviral activity directed at HIV and other enveloped viruses and bacteria has also been described (Orloff et al., 1993; Isaacs and Thormar, 1990). An additional factor that has also been identified in breast milk, possibly a sulphated protein, glycoprotein mucin or glycosaminoglycan, appears to inhibit the binding of HIV to CD4 receptors (Newburg et al., 1992).