Differences between newborn and adult mice in their response to immune thrombocytopenia

Abstract

Background: Sick neonates frequently develop severe thrombocytopenia.

Objective and methods: In order to test the ability of fetal mice to increase their megakaryocyte size and ploidy in response to thrombocytopenia, we injected an antiplatelet antibody (MWReg30) into pregnant mice daily for 7 days, and into nonpregnant adult mice to serve as controls. After that time, platelet counts were obtained and megakaryocytes in the bone marrow, liver, and spleen were stained with anti-von Willebrand factor antibody, individually measured, and quantified.

Results: Our study demonstrated that megakaryocytopoiesis in newborn mice shares many features of human fetal/neonatal megakaryocytopoiesis, including the small size of megakaryocytes. In response to thrombocytopenia, adult mice increased megakaryocyte volume and concentration, primarily in the spleen. Newborn mice, in contrast, increased the megakaryocyte concentration in the spleen, but exhibited no increase in megakaryocyte volume in any of the organs studied. In fact, the megakaryocyte mass was significantly lower in the bone marrow of thrombocytopenic neonates than in age-matched controls.

Conclusions: We concluded that fetuses have a limited ability to increase their megakaryocyte mass in response to consumptive thrombocytopenia, compared to adult mice. These observations provide further evidence for the existence of biological differences between fetal/neonatal and adult megakaryocytopoiesis.

Fig. 1

Platelet counts in newborn and adult mice. One-day-old healthy neonates had significantly lower platelet counts than healthy adult mice. Control mice received daily injections of the antibody vehicle and had platelet counts similar to those of untreated age-matched animals. Mice rendered thrombocytopenic by daily injections of MWReg30 had platelet counts that were significantly lower than age-matched placebo controls. Data are shown as means ± SE M. ∗∗ p < 0.001 vs. placebo control.

Fig. 2

Photomicrograph of megakaryocytes expressing vWF (original magnification ×400) in the liver of control newborn pups (a), thrombocytopenic newborn pups (b), bone marrow from control adults (c), and bone marrow from thrombocytopenic adults (d). The difference in size between neonatal and adult megakaryocytes is clearly evident.

Fig. 3

Box-plots displaying the megakaryocyte (Mk) concentration, size and mass in the bone marrow (BM), liver (Liv) and spleen (Spl) of neonates (a–c), and in the bone marrow and spleen of adult mice (d–f). The box-plot margins represent the 25th–75th percentiles, the whiskers represent the ranges, and the line, the median. N = Normal; T = thrombocytopenic. ∗ p < 0.05 and ∗∗ p < 0.01 versus age-matched controls.

Fig. 4

Megakaryocyte colonies (CFU-Mk) generated from newborn liver and adult bone marrow. Murine newborn liver cells (Liv) generated significantly more megakaryocyte colonies than adult bone marrow cells in culture (mean megakaryocyte colonies per 1 × 10 5 cells plated: 181.1 ± 32.8 for newborn liver versus 26.5 ± 4.3 for adult bone marrow, p < 0.001). There were no significant differences between thrombocytopenic and nonthrombocytopenic age-matched controls in regard to colony counts. Data are presented as mean 8 SEM.