Is a Little Enough? Paucity of Immune Proteins in Serum of Precocial Neonates of a Marine Carnivoran—the Atlantic Grey Seal

Abstract

Mammalian mothers usually provide their offspring with large quantities of immunoglobulins (antibodies) for circulation in blood, either trans-placentally before birth, via colostrum briefly thereafter, or, less commonly, from milk. Neonates of true, phocid seals, however, are peculiarly impoverished in serum immunoglobulins, the levels of which slowly increase but do not reach adult levels by the time of weaning. We investigated whether grey seal (Halichoerus grypus) neonates compensate through an elevation or rapid maturation in levels of serum innate immune factors, namely acute phase and complement proteins. Instead, their sera contained remarkably low levels of acute phase proteins (including C-reactive protein, haptoglobin, hemopexin, ceruloplasmin, orosomucoid), compared to their mothers, that barely increased to adult levels by weaning. For complement, there was a strong demarcation between the early activation and amplification cascade components (present at normal adult levels in pups) and the late lytic membrane attack complex and regulatory proteins (consistently at low relative levels). Phocid neonates therefore differ dramatically from land Carnivorans, such as dogs and cats, in early life immune protection. That neonatal phocids survive this apparent vulnerability to infections between birth and weaning prompts questions as to what other mechanisms protect them, and the adaptive value of their seeming vulnerability.

Mirror image serum lipid carrier protein profiles in pup and lactating mother Atlantic grey seals reflect contrasting resource mobilisation challenges

“…activated by antige n:antibody com plexes [though immunoglobulin levels are unusually low in seal pups (King et al, 1994;Mcgill et al, 2022)], or by C-reactive protein [associated with inflammation and also at low relative levels in grey seal pups (Mcgill et al, 2022)], to trigger cell lysis or opsonisation of pathogens, or initiate inflammatory reactions (Parham, 2021). It could therefore be that the elevated levels of ApoE in pups act to control inappropriate activation of C1q, which would align with our previous finding that complement and certain proteins of the innate immune system are of reduced capacity in grey seal pups (Mcgill et al, 2022). ApoA-1 is similarly involved in aspects of innate immunity, being involved in the control of inflammatory reactions (Yao et al, 2016); it binds bacterial lipopolysaccharide (Ma et al, 2004;Li et al, 2008), and, in humans, it is involved in the killing of trypanosomes (Harrington et al, 2009).…”

“…To avoid desertions by the mothers immediately after birth, the earliest samples were taken on day 2 post-partum. Mothers were tranquilised with an intramuscular mass-adjusted dose of Zoletil 100 (Virbac, Bury St Edmunds, Suffolk, UK), followed by intravenous oxytocin to stimulate milk let-down to provide milk samples as part of a larger study, blood was taken, and given a mass-adjusted intramuscular prophylactic dose of tetracycline after the day 7 and day 18 samples, as reported previously (Lowe et al, 2017;Watson et al, 2020;Watson et al, 2021;Mcgill et al, 2022). Blood was collected by venepuncture of either extradural vein or hind flipper plexus using 3.5in 16G spinal needle or 2in 19G Microlance needle (Becton Dickinson, UK) as appropriate into plain vacutainers and allowed to clot.…”

“…This multiplex comparative proteomics technique provides relative abundances of detected proteins between six samples in one analysis run, and the technique used here is identical to that described in our previous paper (Mcgill et al, 2022). That paper used data acquired from the same three mother/pup pairs as here, having been selected from field observations indicating that birth had occurred within 36 hours after birth, and also that the final sample day occurred on the last day of lactation (pair E) or within three days of its termination (pairs B and D).…”

“…The overall protein concentrations in the sera of grey seal pups increases over time, most clearly due to immunoglobulin and other defence protein changes (Mcgill et al, 2022). We therefore chose to submit equal volumes of serum for TMT proteomics rather than equal amounts of protein in order to more accurately detect changes in individual proteins.…”

“…In grey seals, we find that albumin occurs at similar levels in mothers and pups except the earliest samples in pups (day 2 after birth), in which albumin was substantially higher (Figure 4). This may be residual of high levels of albumin required in uterine life, or reflects other roles for albumin such as regulating the osmotic activity of blood (partly balancing the low total protein levels evident in neonatal pups; (Marquez et al, 2007;Mcgill et al, 2022), or the need for albumin to carry a range of other compounds immediately postpartum.…”