Antigen-induced plaque-forming cell responses in cultures of peripheral blood mononuclear cells of human neonates and infants

The development of antibody responses in the infant

The human infant is a major subject of immunization to prevent infectious disease. A better understanding of immune responses in human infants could lead to more effective immunization. Analysis of individual mechanisms is a prerequisite to understanding the whole response. We have examined the mutation and selection of immunoglobulin genes, mechanisms required for the maturation of antibody affinity. Mutations were rare in cord blood and were not detected in peripheral blood of infants under 10 days of age. Mutations were detected in most blood samples from infants aged 10 days to 2 months but the number of mutations was generally low compared with adults and there was limited evidence of selection. The ability to make and select mutated Ig increased over the 2-8 months period, but did not reach adult levels. Neonates differ from adults in the expression of several components of the immune system that may take part in affinity maturation, including cytokine receptors, antigen receptor and co-stimulator molecules. Thus, the mechanisms required to make high-affinity antibody develop gradually during the first year of life. Possible evolutionary reasons for this are discussed.

The antigen receptor complex on cord B lymphocytes

The neonatal immune system responds to a restricted range of antigens, producing largely IgM antibody of low affinity. Comparison of the components of the B-cell antigen receptor complex shows significantly elevated membrane levels of IgM in neonatal B cells, compared with adult cells. CD79, which acts as the signal transducer for membrane immunoglobulin, is elevated in parallel with IgM, while IgD is elevated to a lesser degree. CD19, CD21, CD22 and CD81, which are all involved in transmitting activation signals when immunoglobulin is engaged, are not elevated. CD32, which is involved in negative regulation of activation, is present at reduced levels on cord B cells. The elevation of B-cell membrane IgM persists during infancy. Neonatal B cells respond in vitro to interleukin-4 (IL-4) by further elevation of membrane IgM levels. The elevated level of membrane IgM may make neonatal B cells easier to trigger by low concentrations of antigen, but in vitro activation and immunoglobulin modulation experiments did not show significant differences between cord and adult B-cell responses to anti-IgM.

Neonatal interleukin-1 beta, interleukin-6, and tumor necrosis factor: cord blood levels and cellular production

In a prospective study, levels of interleukin-1 beta (IL-1 beta), interleukin-6) (IL-6), and tumor necrosis factor (TNF) were measured in a blind fashion in cord blood plasma from 92 neonates by specific immunoassays, and were correlated with the clinical courses of the infants, including type of delivery and perinatal complications. Plasma IL-1 beta concentration was undetectable in infants born by normal vaginal delivery or elective cesarean section but was significantly increased in infants born after induced vaginal deliveries (142 +/- 68 pg/ml) or urgent cesarean section (290 +/- 21 pg/ml; both p less than 0.05 compared with normal deliveries). The IL-1 beta levels were elevated in infants with severe perinatal complications (282 +/- 116 pg/ml; p less than 0.001), whereas TNF and IL-6 levels were not related to these complications. Infants with isolated perinatal infectious complications had elevated levels of plasma IL-6 compared with those of sick neonates without infection (p less than 0.001). In contrast, TNF plasma levels and IL-1 beta production by cord blood leukocytes were decreased in infants with infectious complications alone (both p less than 0.05). These studies suggest that the levels of IL-1 beta, IL-6, and TNF in the cord plasma relate differentially to clinical complications in the perinatal period.

Experimental studies of immunologically mediated enteropathy. VI. Inhibition of acute intestinal graft-versus-host reaction in mice by 2'-deoxyguanosine

We have attempted to investigate the relative roles of specific cytotoxic T lymphocytes (CTL) and allospecific suppressor T cells (Ts) in the systemic and intestinal manifestations of acute graft-versus-host reaction (GvHR) in mice. Treatment of adult (C57B1/10 x DBA/2)F1 (BDF1) mice with the suppressor cell-specific toxin 2'-deoxyguanosine (dGuo) inhibited the weight loss and mortality which normally occur after induction of GvHR and C57Bl donor cells. dGuo also delayed the development of a destructive enteropathy as typified by jejunal villus atrophy. Paradoxically, dGuo completely prevented villus atrophy during an acute GvHR in neonatal (CBA x BALB/c)F1 hosts, despite having only a slight ability to inhibit the systemic disease. In both models, dGuo had no effect on the generation of splenomegaly or anti-host CTL, and dGuo-treated mice with GvHR actually had increased proliferative alterations in the intestine, as assessed by crypt hyperplasia. In parallel, dGuo prevented the loss of NK cells which normally occurs in acute GvHR. Thus dGuo inhibits many of the destructive features of systemic and intestinal GvHR without affecting the development of CTL. We conclude that a dGuo-sensitive mechanism causes the transition from a proliferative to a destructive GvHR.

Interleukin 1 in the in vitro antigen-induced antibody response in the human adult and newborn

Previous studies have shown that in vitro stimulation of human B lymphocytes with antigens such as ovalbumin (OA) induces the formation of small antigen-specific plaque-forming cells (PFC) but precludes the activation of the B cells into full-blown antibody-secreting cells. Insufficient production of T cell-derived growth and differentiation factors appears to be the basis of the phenomenon. Furthermore, cord blood B lymphocytes required 100 times less OA to become activated in vitro into antigen-specific PFC, and the distinct antigen-handling capacities of neonatal monocytes are the basis of this result. We have studied the role of interleukin 1 (IL-1) in the in vitro response of B lymphocytes from either cord blood or adult blood to OA. Addition of IL-1 to the B-cell cultures significantly increased the number of PFC, and about 50% of the plaques now appeared to be high-rate IgM anti-OA-secreting PFC. The IL-1-mediated increase in the PFC response was shown to be based on potentiation of T-helper cell activity. The differences between cord blood and adult blood mononuclear cells in the optimal OA concentration required for effective in vitro activation of B cells remained the same upon addition of IL-1. This result shows that the phenomenon is independent of IL-1.

Ovalbumin-specific human B-cell activation and maturation. The absence of final maturation is due to the incapacity of ovalbumin-activated T cells to produce maturation factors

By means of a panel of monoclonal antibodies it is demonstrated that, in cultures of human peripheral blood mononuclear cells (PBMC) with the T-cell-dependent (TD) antigen ovalbumin (OA), responding B cells are activated from the resting state. The differentiation of the activated B cells to high rate-secreting plasma blasts, however, is arrested in an early activation phase, in which they can be detected as low rate-secreting plaque-forming cells. The arrest does not occur when stimulation with OA occurs in the presence of antigen-nonspecific activation and maturation factors, which are provided in the culture by the anamnestic response to the TD antigen tetanus toxoid.

The in vitro B-cell response to pneumococcal polysaccharides in adults and neonates

In order to gain insight into the relatively late appearance in ontogeny of responsiveness to T-cell independent (TI) antigens, the in vitro human B-cell response to type 4 pneumococcal polysaccharides (PS4, a human TI-2 antigen) was studied. B cells obtained from adults differentiate into anti-PS4 antibody forming cells upon culturing with PS4, but neonatal B cells obtained from cord blood fail to respond. The culture system used does, however, allow the differentiation of B cells reactive with TD antigens, for example ovalbumin. In order to evaluate the concept that in man the anti-PS4 response is derived from a particular B-cell subset we separated adult B cells on the basis of expression of the determinant recognized by the monoclonal antibody FMC7. The anti-PS4 response is found mainly, but not exclusively, in the FMC7+ subset. The selective unresponsiveness of neonatal B cells to TI-2 antigens is not, however, due to the absence of FMC7+ B cells because, unlike adult blood B cells of which about 50% are FMC7+, 100% of neonatal B cells are FMC7+.