Postnatal changes of CD45 expression in peripheral blood T and B cells

CD45RA, CD8β, and IFNγ Are Potential Immune Biomarkers of Human Cognitive Function

There is increasing evidence that in humans the adaptive immunological system can influence cognitive functions of the brain. We have undertaken a comprehensive immunological analysis of lymphocyte and monocyte populations as well as of HLA molecules expression in a cohort of elderly volunteers (age range, 64–101) differing in their cognitive status. Hereby, we report on the identification of a novel signature in cognitively impaired elderly characterized by: (1) elevated percentages of CD8+ T effector-memory cells expressing high levels of the CD45RA phosphate receptor (Temra^hi); (2) high percentages of CD8+ T cells expressing high levels of the CD8β chain (CD8β^hi); (3) augmented production of IFNγ by in vitro activated CD4+ T cells. Noteworthy, CD3+CD8+ Temra^hi and CD3+CD8β^hi cells were associated with impaired cognition. Cytomegalovirus seroprevalence showed that all volunteers studied but one were CMV positive. Finally, we show that some of these phenotypic and functional features are associated with an increased frequency of the HLA-B8 serotype, which belongs to the ancestral haplotype HLA-A1, Cw7, B8, DR3, DQ2, among cognitively impaired volunteers. To our knowledge, this is the first proof in humans linking the amount of cell surface CD45RA and CD8β chain expressed by CD8+ Temra cells, and the amount of IFNγ produced by in vitro activated CD4+ T cells, with impaired cognitive function in the elderly.

Stem Cell Transplantation in the Fetus

BACKGROUND

In utero transplantation (IUT) of hematopoietic stem cells has the potential to treat a large number of hematologic and metabolic diseases amenable to partial replacement of the hematopoietic system.

METHODS

A review of the literature was conducted that focused on the clinical and experimental experience with IUT and, in this context, the development of the hematopoietic and immune systems.

RESULTS

Successful application of IUT has been limited to the treatment of various types of immunodeficiencies that affect lymphocyte development and function. Other congenital defects such as the thalassemias have not resulted in clinically significant engraftment. Recent efforts at understanding and overcoming the barriers to engraftment in the fetus have focused on providing a selective advantage to donor stem cells and fostering immune tolerance toward the donor cells. The critical cellular components of the graft that promote engraftment and tolerance induction are being evaluated in animal models. Improvements in engraftment have resulted from the inclusion of T cells and/or dendritic cells in the graft, as well as a strategy of combined prenatal and postnatal transplantation.

CONCLUSIONS

The advantages, necessity, and benefits of early treatment will continue to encourage development of IUT as a means to treat hematopoietic and other types of birth defects.

Ontogenic changes in CD95 expression on human leukocytes: prevalence of T-cells expressing activation markers and identification of CD95-CD45RO+ T-cells in the fetus

The ontogeny of the human immune system was studied by analyzing fetal and adult tissues for the presence of various lymphocyte populations and activation/maturation markers. CD95 (fas) was expressed in hematopoietic tissues during the final stages of development of monocytes, granulocytes, NK cells and T cells, but to a much lesser extent on B cells. In the periphery, CD95 expression declined on granulocytes and NK cells. CD95 was expressed at a higher level on CD45RA+ peripheral T-cells in the fetus than in the adult. Contrary to the belief that most fetal T-cells are naïve or resting, a notable number of CD45RO+ T-cells were observed as well as an unique CD95-CD45RO+ population. Activation markers CD25, CD122, CD69 and CD80 were also present on fetal T-cells. These findings indicate that in the initial weeks following thymic maturation, a high frequency of T-cells is activated in the periphery of the fetus.

In utero priming of allergen-specific helper T cells

BACKGROUND

Allergic diseases are major health problems in developed countries. Cord blood mononuclear cells (CBMC) at birth can proliferate after stimulation with allergen and this has led to the widespread view that the sensitization of the fetal immune system by allergens is a key determinant in establishing immunological bias towards allergy. However, the notion that the immune system can be primed by allergen in utero remains unproven. Determination of the CD45 isoform of responding T helper cells is an established method of determining the activation status of responding T helper cells because unsensitized cells express CD45RAhigh and previously sensitized cells CD45ROhigh.

OBJECTIVE

To determine if sensitization of allergen-specific T helper cells can occur in utero by determining the CD45 isoform of CBMC proliferating in response to allergen.

METHODS

CBMC proliferative responses were measured after stimulation in culture with a panel of allergens, mitogen and control antigen. To ascertain whether any responding T helper cells had been primed in utero, depletion experiments established whether they carried the CD45ROhigh marker of previous activation or the CD45RAhigh marker of unstimulated T cells.

RESULTS

CBMC from a high proportion of 223 randomly selected neonates were stimulated to proliferate in vitro by allergens, with 76% responding to timothy grass pollen. In 50% of such responses to timothy grass, the CD45 isoform of the T cells that proliferate indicated that they had been previously activated. However, the remaining 50% of responses to timothy grass were mediated by previously unstimulated T cells. Proliferative responses mediated by CBMC sensitized in utero tended to be greater in magnitude than those mediated by unsensitized cells (P = 0.08). Seventy-five per cent of CBMC samples proliferated after stimulation with mycobacterial PPD and, as in BCG-vaccinated adults, all such CBMC proliferative responses at birth were predominately mediated by sensitized cells.

CONCLUSION

Allergen- and antigen-specific Th cells can be primed in utero.

Polyunsaturated fatty acids and T-cell function: implications for the neonate

Infant survival depends on the ability to respond effectively and appropriately to environmental challenges. Infants are born with a degree of immunological immaturity that renders them susceptible to infection and abnormal dietary responses (allergies). T-lymphocyte function is poorly developed at birth. The reduced ability of infants to respond to mitogens may be the result of the low number of CD45RO+ (memory/antigen-primed) T cells in the infant or the limited ability to produce cytokines [particularly interferon-y, interleukin (IL)-4, and IL-10. There have been many important changes in optimizing breast milk substitutes for infants; however, few have been directed at replacing factors in breast milk that convey immune benefits. Recent research has been directed at the neurological, retinal, and membrane benefits of adding 20:4n-6 (arachidonic acid; AA) and 22:6n-3 (docosahexaenoic acid; DHA) to infant formula. In adults and animals, feeding DHA affects T-cell function. However, the effect of these lipids on the development and function of the infant's immune system is not known. We recently reported the effect of adding DHA + AA to a standard infant formula on several functional indices of immune development. Compared with standard formula, feeding a formula containing DHA + AA increased the proportion of antigen mature (CD45RO+) CD4+ cells, improved IL-10 production, and reduced IL-2 production to levels not different from those of human milk-fed infants. This review will briefly describe T-cell development and the potential immune effect of feeding long-chain polyunsaturated fatty acids to the neonate.

UDP-GlcNAc 2-epimerase: a regulator of cell surface sialylation

Modification of cell surface molecules with sialic acid is crucial for their function in many biological processes, including cell adhesion and signal transduction. Uridine diphosphate-N-acetylglucosamine 2-epimerase (UDP-GlcNAc 2-epimerase) is an enzyme that catalyzes an early, rate-limiting step in the sialic acid biosynthetic pathway. UDP-GlcNAc 2-epimerase was found to be a major determinant of cell surface sialylation in human hematopoietic cell lines and a critical regulator of the function of specific cell surface adhesion molecules.

Conformational changes in CD45 upon monoclonal antibody crosslinking

The CD45 protein tyrosine phosphatase is expressed in different isoforms that result from alternative splicing of three exons (A, B, and C) encoding regions near the N-terminus of the extracellular part of the molecule. We describe here a novel epitope on the N-terminal end of CD45 that is recognized by the MAb BL-TSub/2. Crossblocking studies showed that BL-TSub/2 and UCHL1 (CD45RO) binding sites are partially overlapping. However, in marked contrast to the CD45RO epitope, protease treatment of cells strongly diminished BL-TSub/2 binding. Similar to the UCHL1 epitope, the BL-TSub/2 binding site involves carbohydrate moieties, since neuraminidase treatment abrogated the reactivity of the MAb. Markedly, preincubation of cells with both CD45 common and CD45RA MAb induced a pronounced increase of BL-TSub/2 binding. This latter finding suggests that crosslinking of the CD45 molecule leads to conformational changes that could influence association of the molecule with putative ligands.

CD45 (leucocyte common antigen) expression in T and B lymphocyte subsets

CD45 is the dominant tyrosine phosphatase in haematopoietic cells and can modulate the effects of many other signaling molecules by dephosphorylation. The extracellular portion of CD45 has considerable variability due to differential splicing and glycosylation. This may allow for interactions with a variety of ligands expressed on interacting cells or on the same cell surface. Monoclonal anti CD45 antibodies that are reactive with epitopes that result from differential splicing and glycosylation can distinguish between cell populations that differ in maturation and function. These reagents can be used in the immunophenotyping of hematopoietic malignancies as well as in immunodeficiencies and autoimmune diseases. Several studies have shown that different anti CD45 reagents have different activating or inhibiting effects in vitro on a variety of T and B cell activation events. There are some indications that anti CD45 reagents can also selectively modify lymphocyte function in vivo. Such applications could potentially allow for the selective upregulation and down regulation of lymphocyte functions in a variety of immunologically mediated diseases.