Anti-HTLV-1/2 IgG Antibodies in the Breastmilk of Seropositive Mothers

Abstract

Background: HTLV-1/2 mother-to-child transmission (MTCT) is an important route for the maintenance of HTLV-1/2 within populations and disproportionally contributes to the burden of HTLV-1-associated diseases. Avoidance of breastfeeding is the safest recommendation to prevent MTCT. Due to the benefits of breastfeeding, alternative methods that would allow seropositive mothers to breastfeed their babies are needed. There is limited knowledge about HTLV-1/2 infection and breastmilk.

Methods: Paired blood and milk samples collected from HTLV-1/2 seropositive mothers were tested for HTLV-1 proviral load (PVL) quantification and for the detection of anti-HTLV-1/2 IgG.

Results: All breastmilk samples had detectable anti-HTLV-1/2 IgG. HTLV-1/2 proviral DNA was detected in all samples except for one. HTLV-1 PVL and IgG binding ratio (BR) was similar in milk and plasma. However, antibody titer was significantly higher in blood (Median (95%CI): Milk:128 (32-512); Plasma:131,584 (16,000-131,584), p < 0.05). There was a strong correlation between HTLV-1 PVL, anti-HTLV-1/2 IgG BR, and titer when comparing milk and blood. PVL did not correlate with antibody BR nor titer in blood or milk.

Conclusions: Anti-HTLV-1/2 IgG are present in milk in the same proportion as blood but in lower quantity. PVL in milk correlates with blood.

Keywords: HTLV-1; HTLV-2; antibodies; breastmilk; mother-to-child transmission; vertical transmission.

Figure 1

Anti-HTLV-1/2 IgG and proviral load in plasma and milk samples. (A) Comparison of anti-HTLV-1/2 proviral load (PVL) in milk and plasma measured by real-time PCR. (B) Comparison of anti-HTLV-1/2 IgG binding ratio (BR) in milk and plasma using anti-HTLV-1/2 IgG capture ELISA assay. (C) Comparison of anti-HTLV-1/2 IgG titer in milk and plasma serially diluted in 1:2. Y axis is in log2 scale. Each dot represents a sample. Horizontal bars represent median. Wilcoxon paired test was used to compare groups and p values are shown. (D) Correlation between HTLV-1/2 PVL in peripheral blood mononuclear cells (PBMCs) and milk. (E) Correlation between anti-HTLV-1/2 IgG BR in plasma and milk. (F) Correlation between anti-HTLV-1/2 IgG titer in plasma and milk. Each dot represents a sample. Correlation coefficient (Spearman test) and p values are shown.

Figure 2

Titration of anti-HTLV-1/2 IgG in paired plasma and milk samples. Paired plasma and blood samples were serial diluted in crystalloid buffer and tested in the anti-HTLV-1/2 IgG capture ELISA assay. Horizontal black dashed line shows the assay cut-off. Plasma samples are represented by a dashed line and milk samples by a continuous line. Each individual is represented by a different color. Light and dark green shows samples from the same patient collected after distinct pregnancies. Light and dark blue are samples from the same patient collected at different time-points after the same pregnancy. A black, continuous line shows the negative control.

Figure 3

Correlation between HTLV-1/2 proviral load and anti-HTLV-1/2 IgG antibodies. Milk and plasma samples were tested using real-time PCR for the determination of HTLV-1/2 proviral load and with anti-HTLV-1/2 IgG capture assay for the determination of the binding ratio (BR) and the antibody titer. Correlation coefficient was calculated using Spearman test. The results are shown with their respective p value. Correlation between anti-HTLV-1/2 IgG BR and titer in blood (A) and in milk (B); Correlation between anti-HTLV-1/2 IgG BR and HTLV-1/2 PVL in blood (C) and in milk (D); Correlation between anti-HTLV-1/2 IgG Titer and HTLV-1/2 PVL in blood (E) and in milk (F).

Figure 4

Graphic illustration of the hypothesis for higher risk of HTLV-1/2 infection with long-term breastfeeding. High levels of anti-HTLV-1 antibodies are transferred via placenta during pregnancy. These antibodies contribute to protection against intra-uterine infection. After birth, those antibodies passively transferred in-utero decrease. The level of antibodies in milk is low. As HTLV-1 is present in breast milk, there is a cumulative exposure to HTLV-1. The hypothesis is that this will culminate in increasing risk of HTLV-1 transmission with long-term breastfeeding. Image Created with BioRender.com in June 2021.