Host cytokines and immune responses in pregnancy associated transmission of arrested hookworm larvae

by 1975- Trivedi, Shweta

TRIVEDI, SHWETA. Host cytokines and immune responses in pregnancy associated transmission of arrested hookworm larvae (Under the direction of Dr. Prema Arasu) Over one billion people worldwide are infected with the hookworms, Necator and Ancylostoma spp. Upon entry into the host, infective larvae (third stage L3 which are free-living and non-feeding) typically mature into blood-feeding adults in the small intestines. An important aspect of the life cycle for A. duodenale (humans) and A. caninum (dogs) is the propensity for L3 to undergo a temporary state of developmental arrest in the host. In female hosts, these tissue-arrested L3 reactivate during pregnancy and are transmitted to the neonates through milk. During pregnancy transforming growth factor (TGF)-? is apparently upregulated in host tissues including the mammary gland. Studies from the free-living nematode Caenorhabditis elegans show that TGF-? and insulin-like signaling pathways regulate larval arrest and resumption of development. Similar signaling pathways are proposed in the pregnancy-associated reactivation of arrested Ancylostoma larvae. We have previously used an in vitro assay to demonstrate that recombinant human TGF-? can stimulate a feeding response in tissue-arrested A. caninum L3 larvae. We speculate that host factors like TGF-? and pregnancy hormones such as estrogen and prolactin signal arrested L3 larvae to resume development. To facilitate analyses of mechanisms of reactivation and transmission in vivo, we have utilized a mouse model of A. caninum infection; mice serve as an excellent model because infective L3 do not develop into adults but migrate to different somatic tissues and arrest, later reactivating during the periparturient period to transmit through milk. Skeletal muscle and mammary gland are the major tissues of interest during this process of arrest, reactivation and transmission. We investigated TGF-?1, TGF-?2 and IGF-1 serum and transcript cytokine profiles during late pregnancy, early lactation and midlactation in mice infected with A. caninum to correlate their levels with the transmammary transmission of the larvae to the nursing pups. An in vitro co-culture system was also developed in an attempt to mimic in vivo conditions for assessing the effects of TGF-? and, estrogen and prolactin on larval reactivation. A. caninum L3 were co-incubated with primary skeletal muscle and mammary epithelial cells in a Transwell ® setup and larval reactivation was measured utilizing the in vitro feeding assay. Additionally, the immune responses during concurrent pregnancy and helminthic infection were assessed given that both conditions are known to be biased towards a T helper (Th)-2 type of response. Serum and transcript levels of IFN-? (representative of the Th1 arm of the immune response) and IL-4 (for Th2) were measured in skeletal muscle, mammary gland and spleen during pregnancy and A. caninum infection in the mouse. These findings which are based upon serum and transcript levels suggest that host-derived TGF- ?1 and IGF-1 may play roles in the reactivation and transmission of arrested A. caninum larvae; levels of TGF- ?2 did not however, show a correlation with the timepoints of pregnancy and lactation associated with larval reactivation and transfer. Also, a Th2-like response characterized by elevation in IL-4 transcript levels was observed in skeletal muscle while a mixed Th1/Th2 profile was observed in mammary gland when comparing the different permutations of infection with A. caninum versus pregnancy/lactation in BALB/c mice.