Self and nonself: duality of immune system

The multi-differentiation potential of peripheral blood mononuclear cells

Peripheral blood is a large accessible source of adult stem cells for both basic research and clinical applications. Peripheral blood mononuclear cells (PBMCs) have been reported to contain a multitude of distinct multipotent progenitor cell populations and possess the potential to differentiate into blood cells, endothelial cells, hepatocytes, cardiomyogenic cells, smooth muscle cells, osteoblasts, osteoclasts, epithelial cells, neural cells, or myofibroblasts under appropriate conditions. Furthermore, transplantation of these PBMC-derived cells can regenerate tissues and restore function after injury. This mini-review summarizes the multi-differentiation potential of PBMCs reported in the past years, discusses the possible mechanisms for this multi-differentiation potential, and describes recent techniques for efficient PBMC isolation and purification.

Stem cell fusion as an ultimate line of defense against xenobiotics

There are several indications that the potential of stem cells to fuse with somatic cells is extremely high and, what's more exciting, in some instances goes as far as reprogramming and/or rescuing altered cells. It remains unclear, however, how frequent this mechanism is and what patho-physiological role it might play in nature. A plausible hypothesis, discussed in this paper, suggests that stem cell niches might provide a safeguard for the intact genome and epigenome. By fusing with somatic de-differentiated cells, stem cells might consent epigenetic reprogramming and/or genetic recovery of genes which otherwise could drive altered cells to malignancy. If the many sophisticated mechanisms of metabolism, cell repair, programmed cell death and tissue regeneration should fail, stem cells might represent a final attempt to recover dedifferentiated cells to avoid inflowing in cancer. In the current reappraisal of the different mechanisms of defense against xenobiotics, even the incidence of cancer itself is considered an evolving mechanism which, through a kind of programmed death of individuals exhibiting defective mutations, favors advancement of the phenotypes which adapt best. Additionally, with regard to the mechanisms of transmitting somatic mutations, based on stem cells' capacity to migrate and to fuse, here it is speculated that stem cells might be capable of carrying acquired somatic mutations from peripheral tissues to the gonads, and transmit that information into the germinal line. If appropriately demonstrated, these mechanisms might delineate a novel therapeutic area to be explored. The use of stem cells to reprogram/recover irreversibly damaged cells or to transmit beneficial mutations might be a valuable therapeutic approach in the future.

Induction of stem cell-like plasticity in mononuclear cells derived from unmobilised adult human peripheral blood

Undifferentiated pluripotent stem cells with flexible developmental potentials are not normally found in peripheral blood. However, such cells have recently been reported to reside in the bone marrow. Herein are reported methods of inducing pluripotency in cells derived from unmobilised adult human peripheral blood. In response to the inclusion of purified CR3/43 monoclonal antibody (mAb) to well-established culture conditions, mononuclear cells (MNC) obtained from a single blood donor are converted into pluripotent haematopoietic, neuronal and cardiomyogenic progenitor stem cells or undifferentiated stem cells. The haematopoietic stem cells are CD34+, clonogenic and have been shown to repopulate non-obese diabetic/severe combined immunodeficient (NOD/SCID) mice. The neuronal precursors transcribe the primitive stem cell markers OCT-4 and nestin, and on maturation, differentially stain positive for neuronal, glial or oligodendrocyte-specific antigens. The cardiomyogenic progenitor stem cells form large bodies of asynchronously beating cells and differentiate into mature cardiomyocytes which transcribe GATA-4. The undifferentiated stem cells do not express haematopoietic-associated markers, are negative for major histocompatibility complex (MHC) class I and II antigens, transcribe high levels of OCT-4 and form embryoid body (EB)-like structures. This induction of stem cell-like plasticity in MNC may have proceeded by a process of retrodifferentiation but, in any case, could have profound clinical and pharmacological implications. Finally, the flexibility and the speed by which a variety of stem cell classes can be generated ex vivo from donor blood could potentially transfer this novel process into a less invasive automated clinical procedure.

The measurement of stress-related immune dysfunction in psychoneuroimmunology

In recent years there has been a dramatic increase in research dedicated to the psycho-behavioural modulation of immune function, i.e. the field of Psychoneuroimmunology (PNI). This has led, necessarily, to the use of several in vitro and in vivo techniques in attempts to delineate the relationship between these two phenomena. However, since the field's inception, considerable uncertainty has existed over the significance of the immune outcomes detected and this has been compounded by the equivocal nature of some of the published data. A great deal of this uncertainty could, however, be overcome if a clearer understanding was achieved on the advantages and limitations conferred by the manifold immune assays described in the literature. This would, in turn, encourage their more appropriate use within PNI. Hence, in this review we describe the rationale behind, and offer an evaluation of, some of the more frequently used in vitro and in vivo immunological and virological techniques. We hope that a clear understanding of the rationale behind such assays and their inherent advantages and limitations will inform the discussion of the significance of stress-related immune impairment.

Major histocompatibility complex as an antigen pump: self-declaration in somatic cell society

Self-recognition by the immune system is a basic mechanism of vertebrates. Mechanisms of antigen presentation by somatic cells are based on the coupling of small peptides produced in cytoplasm and major histocompatibility complex major histocompatibility complex. The antigen pumps, including major histocompatibility complex, can present various internal molecules which are possible targets of autoimmunity, using a peptide binding mechanism. The antigen pump can transfer external signals by autoantibody and cellular immunity without a specific receptor system. This self-declaration mechanism continuously presents 'self' rather than 'non-self'. It is qualitatively impossible to differentiate self antigens from non-self antigens in this process at all. Somatic cell society is non-self for germ line DNA, since germ line DNA is symbiotic with somatic cell society. Consequently, non-self can be recognized through self-declaration.

Transplantation and chimera as extended self

Transplantation can be considered as an artificial reconstitution of symbiosis called chimera, since the donor and recipient carry different DNAs. In successful transplantation, engrafted tissues and cells should be recognized as self by the immune system, as shown in external pathogens. The external milieu introduced by transplantation and infection can only be immunologically recognized as self when it forms a symbiotic relationship with somatic cell society. Immunological identity is a posteriori educated recognizing immunological self and genetic self may be ignored in self-recognition. For example, transplanted bone marrow immunocytes recognize somatic cell society which is selected previously by other immunological standards as self. Dissociation between genetic self and immunological self originates in the development and differentiation of multicellular organisms a priori, since alteration of DNA sequences is necessary in the development and differentiation of multicellular organisms and symbiosis is the essential nature of it.

Acquired immune deficiency syndrome caused by hyperimmunity

Normal immunocytes including T and B cells are equilibrated by a reciprocal attacking mechanism called a network. Continuous disequilibrium of this network results in general immunodeficiency with oligo- and polyclonal hyperimmunity, for example, T-cell activation due to spontaneous reticuloendotheliosis, paraneoplastic autoimmune syndromes, and human immunodeficiency virus infection. In these disorders, reciprocal self-reactivity, including autologous graft-versus-host reaction, plays a role in the immunodeficiency. A priori self-targeting immunity is a key mechanism to explain autoimmunity in the acquired immunodeficiency syndrome. In the treatment of the immunodeficiency due to hyperimmunity, I propose immunological suppression by agents and reconstitution of the network by bone-marrow transplantation.

Origin of blood-group antigens: a self-declaration mechanism in somatic cell society

Blood-group antigens have been developed as a self-declaration mechanism in higher organisms, since blood cells carry different DNA from that of germ-line cells, and their selfishness must be strictly limited. If not, symbiosis between somatic DNA and germ-line DNA cannot be maintained since blood cells can express autonomy programmed within themselves. For the sake of maintenance of symbiosis, this self-declaration is not limited to blood cells and all somatic cells need a self-plural declaration mechanism such as blood-group antigens. Differentiation and development including induction and inhibition also depend on the self-declaration--recognition mechanism.