Neonatal immunity and somatic mutation

Neonatal animals are able to mount an effective immune response, both humoral and cellular, when immunized using conditions that maximize stimulation of antigen presenting cells, T cells, and B cells. In adults, somatic mutation is a key feature of the humoral immune response because it contributes to the generation of high affinity memory B cells. Recent evidence that B cells in neonatal mice and human infants can somatically mutate their immunoglobulin heavy chains suggests that neonates can utilize somatic mutation not only to diversify their restricted germline antibody repertoire, but also to improve upon this repertoire by the generation of B cells which can produce higher affinity antibodies. By extrapolation, if vaccination of children early in life resulted in somatic mutation and affinity maturation, this could provide a more protective antibody response to childhood diseases.     

Neonatal tolerant immunity for vaccination against autoimmunity

Autoimmunity arises when the immune system no longer tolerates self and precipitates lymphocyte reactivity against our own antigens. Although the developing T cell repertoire is constantly purging, self-recognition events do exist when such tight control is evaded and autoreactive lymphocytes escape the thymus (the sites of T cell development) and migrate to the periphery. Upon activation these autoreactive cells may exert aggressive behavior toward one's own tissues and organs leading to autoimmune disease. Multiple sclerosis, Rheumatoid arthritis, and type I diabetes are autoimmune diseases mediated by autoreactive T cells. A logical approach to prevent such autoimmunity would be to reprogram those lymphocytes to tolerate the self antigen. Injection of antigen at the neonatal stage promotes a state of tolerance such that successive encounter with antigen does not precipitate aggressive reactions. The mechanism underlying neonatal tolerance involves priming of T cells whose effector functions do not cause inflammatory reactions upon recognition of antigen but rather induce protective immunity. This form of tolerant immunity provides an attractive strategy for vaccination against autoimmunity. Herein, it is shown that neonatal exposure to a self-peptide-immunoglobulin chimera drives a tolerant immunity toward the self-peptide and protects against the autoimmune disease, experimental allergic encephalomyelitis.     

Neonatal haemochromatosis

Four cases of neonatal haemochromatosis presenting as fulminant hepatic failure in the newborn were diagnosed by autopsy. In all four cases the diagnosis was made by histochemical demonstration of excessive iron deposition in hepatocytes and extrahepatic parenchymal cells, particularly pancreatic acinar epithelium, thyroid follicular epithelium and distal renal tubules. No haemosiderin was detectable in the extrahepatic mononuclear-phagocytic cells of the spleen, lymph nodes and bone marrow. The liver was the most severely affected organ. The hepatic haemosiderosis was associated with massive hepatocellular necrosis of prenatal onset in three patients, one of whom showed formation of regenerative nodules, establishing true congenital cirrhosis. Other inconstant findings included giant cell transformation, diffuse sinusoidal fibrosis with segregation of small groups of hepatocytes and cholestasis with pseudoacinar change of liver cell plates. The fetal liver disease had its onset in the late second trimester of pregnancy and was reflected clinically by severe panhypoproteinaemia with non-immune hydrops; hyperbilirubinaemia and haemorrhagic diatheses were apparent in the newborn. Neonatal haemochromatosis is a metabolic disorder, probably of autosomal recessive inheritance. The site and nature of the basic defect remain uncertain. Pathologists should be aware of this condition and its potential recurrence in subsequent pregnancies.     

Neonatal hemochromatosis

Neonatal hemochromatosis is a specific entity in the spectrum of pediatric liver disease. The clinical course is characterized by progressive deterioration, leading to death within a few days to weeks. The pathologic changes are hepatic fibrosis with massive iron accumulation in hepatocytes. Lesser amounts of iron are found in parenchymal cells of the endocrine organs (adrenal, thyroid, pancreas, pituitary), the heart, and renal tubules. Little iron is present in cells of the reticuloendothelial system. The morphologic pattern thus resembles that of adult idiopathic hemochromatosis. Iron accumulation is a relatively specific finding, as shown by a review of a series of pediatric autopsy cases. Premortem diagnosis of this disease has been made only rarely, and little information is available on laboratory parameters. Recognition of this entity in living neonates is necessary for better understanding of its pathogenesis and treatment.     

Neonatal Legionnaires'Disease

A neonatal case of legionnaires'disease (LD) is reported. A male neonate was admitted to our hospital with high fever and dyspnea, which had started 5 days after birth, and died due to severe pneumonia at 10 days old. An autopsy revealed small areas of granular consolidation scattered diffusely in the bilateral lungs. Microscopic examination of the lungs showed mainly lobularly distributed pneumonia. Extensive exudation of macrophages and neutrophils was observed in the terminal respiratory tract and alveolar spaces. Warthin-Starry and Gimenez staining and electron microscopy detected many coccobacilli in the cytoplasm of exudated macrophages and neutrophils. Immunofluorescence staining using antiserum against Legionella pneumophila , serogroup 1, showed a positive reaction. Bacteriological examinations of aspirate from the respiratory tract and autopsied lung tissue confirmed the presence of Legionella pneumophila , serogroup 1. Extrapulmonary LD was not detected. LD usually affects aged or immunocompromised hosts, but there was no evidence of immune deficiency in this case. Pediatric cases of LD have rarely been reported, and a survey of the literature revealed few neonatal cases. The present case may alert neonatologists and other medical personnel to the possibility of neonatal LD infection.     

Neonatal lupus

Congenital heart block (CHB), defined as an atrioventricular block diagnosed in utero, at birth, or within the neonatal period (0-27 d after birth), is a rare disorder closely linked to transplacental transport of maternal antibodies anti-Ro/SSA and anti-La/SSB. These antibodies may induce a myocarditis, or interact directly with calcium channel proteins with disturbance of transmembrane signaling at the level of the conduction tissue, or interfere with apoptosis. Depending on the severity of the process, the fetus may die in utero or a few days after birth or survive to the perinatal period and have a near-normal life; in most survivors a pace-maker must be implanted. Skin lesions, haematological disorders, and hepatic cholestasis are other transient clinical features of the syndrome. Sinus bradycardia and QT interval prolongation may be observed as well in babies born from anti-Ro/SSA positive mothers. The risk of recurrence of complete block ranges from 10-17%. Most of the mothers are asymptomatic at delivery and are identified only by the birth of an affected child. Their long-term outcome generally is more reassuring than previously assumed and arthralgias and dry eyes are the most common symptoms. A standard therapy for blocks detected in utero still does not exist. The prevalence of complete CHB in newborns of anti-Ro/SSA positive women and with known connective-tissue disease was 2%. Serial echocardiograms and obstetric sonograms, performed at least every 2 wk starting from the 16 wk gestation, are recommended in anti-Ro/SSA positive pregnant women.