Feasibility and Acceptability of an Online Positive Affect Intervention for Those Living with Comorbid HIV Depression.

Positive affect has unique beneficial effects on psychological and physical health, independent of the effects of negative affect. Interventions that explicitly target positive affect show promise for improving health outcomes in a number of chronic illnesses. In this article, we present pilot data on the acceptability and feasibility of an online intervention to increase positive affect in those living with comorbid human immunodeficiency virus (HIV) and depression. The intervention was rated both acceptable and feasible by participants. Six of nine participants completed the intervention and the subsequent follow-up assessment and a post-intervention phone call. We also present outcomes of planned comparisons of intervention effects on emotion, which indicate that positive affect increased significantly in the intervention group. Based upon results of the current study, future research should continue the development of positive affect interventions for people living with comorbid HIV and depression.

TCR-pMHC interactions: Two peptide repertoires-one signal.

The peptide (P) ligand seen by the TCR is presented by an MHC-encoded restricting element (R). Peptide is viewed from two perspectives, that of the TCR and that of R. The TCR looks at P using an anti-P site that is somatically generated and selected, whereas R looks at P using a binding site that is germline generated and selected. The two segments of P, the one viewed by the TCR, the other viewed by R divide P into two repertoires, Ptcr and Pr that are recognized independently but function cooperatively. The consequences of this for an understanding of TCR specificity and signalling as well as the role of differential processing are analysed. It is ironic that from the point of view of the immunologist, the TCR is highly polyreactive recognizing over a million peptides, whereas from the point of view of the immune system, the TCR is highly specific recognizing essentially only one epitope.

Somatic diversification of the B cell repertoire requires two cell subsets.

Evolution found itself in a Catch-22 situation when selecting for the somatically derived paratopic repertoire of the humoral immune system. The B cell BCR repertoire can only be somatically diversified from a substrate of paratopes that is encoded in the germline. In order for the cells expressing that substrate to also be a target of germline selection, their BCRs must, independently, be of selective value by being expressed in a functionally important way in each individual. A somatically derived repertoire scrambles this substrate so that its specificities are lost, making it unselectable in the germline. Consequently, evolution faced an incompatibility. Here, we explore what it takes to resolve it.

A Commentary on a Workshop 'To Reveal the Foundational Concepts of Immune Regulation' (i.e. Tolerance).

A summary of the workshop with its laudatory goal 'to reveal the foundational concepts in immunology' was recently published in SJI with an invitation to outsiders to comment. In the end, a foundational concept is one upon which we can all agree. This requires debate and meaningful experimentation. The goal of this commentary is to provide some of that. Most of immunology is description of an observation (i.e. a fact). However, what ties all the facts together as a discipline is theory or conceptualization that gives a general context to observation and predicts the next step. This is what is meant by 'foundational concepts'.

Giving Context to Non-self-marker Theories of Immune Responsiveness.

In 2001, long ago by modern standards, Matzinger changed the emphasis of her Danger theory from one that downplayed the self-non-self discrimination to one that concerned itself with the regulation of effector class. This gave her theory a measure of validity that the other non-self-marker theorists have yet to confront. However, precision and clarity are still lacking.

Thoughts on Positive Selection in Thymus.

Any analysis of the mechanism of signalling during positive selection in the thymus is dependent on one's model of the TCR-ligand interaction. To date, thinking about mechanism has been dominated by what might be termed the Standard (or Centric) model, which is based on analogy between the BCR and the TCR. As the present analysis is an independent rationalized view of the TCR-ligand interactions, it permits a more balanced view of positive selection. The goal here was to explore this alternative to the Standard model.

Contemplating Bretscher's View that the Tritope Model is 'Implausible'.

There is, at present, only two models of the TCR structure-function relationship. These are referred to here as the Standard (Centric) model and the Tritope model. While I have argued that the Standard model is untenable and proposed the Tritope to replace it, Bretscher has argued that the Tritope model is 'implausible' and throws his support for the Standard model. This essay analyses the implausibility argument concluding that it is unfounded.

Thoughts engendered by Bretscher's Two-step, Two-signal model for a peripheral self-non-self discrimination and the origin of primer effector T helpers.

There are three questions under re-examination here that have been inspired by Bretscher's 'Two-step, Two-signal' model. First, what is the nature of the steps required in order for antigen-responsive cells to become effectors? Second, how does the immune system get started? Third and the most troublesome, what is the mechanism that relates the delivery of the two signals? To answer the first question, Bretscher proposes a pathway that I will place in another context by comparing it with what had been envisaged under the Associative Recognition of Antigen (ARA) model. The second question, how does the immune system gets started, is crucial to our understanding of the self-non-self discrimination. This problem boils down to, what is the origin of the first effector T helper (eTh) cells required to activate all antigen-responsive cells including the T helpers themselves (the primer problem)? To deal with this question, I proposed an antigen-independent pathway to primer eTh. Bretscher presents us with an antigen-dependent pathway to primer eTh. As competing models are precious in clarifying thinking and in guiding experimentation, I felt it important to reanalyse the two models and look for ways to decide between them. The third question deals with the requirement for and the mechanism of associative (linked) recognition of antigen (ARA). The concept of ARA is so compelling at both the experimental and theoretical levels that to save it, a new perspective will be introduced.

Challenging the Tritope Model of T cell receptor structure-function relationships with classical data on 'super' and 'allo-MHC' antigens.

The response of the immune system to allo-MHC-encoded antigens and Mls 'superantigens' has been experimentally analysed in detail, but the data have not been coupled to a theoretical framework. It should therefore be instructive to see how well the newly proposed Tritope Model of TCR structure-function relationships deals with the signalling interactions between the TCR and the above antigens. We will pay heed to William Bateson's admonition, 'treasure the exceptions', by showing how a meaningful theory interrogates the data with the same validity that the data interrogate the theory. The concordances, as well as the contradictions, with the Tritope Model are a test of its heuristic value.

Meanderings into the regulation of effector class by the immune system: derivation of the trauma model.

The pathway of immune system behaviour can be divided into three modules, each with its own logic and database. The modules are related in that they feed sequentially into each other for function. The modules are (1) the generation of the recognitive repertoire; (2) the sorting of the repertoire by purging it of anti-self; and (3) the coupling of the residue, anti-nonself, appropriately to the biodestructive and ridding effector functions. While both the generation and sorting of the repertoire have been intensively investigated and are well understood in terms of firm theoretical frameworks, the understanding of Module 3, the regulation of effector class, is patchy. This essay is an attempt to define the elements required for an understanding of Module 3 and that leads us to propose the Trauma Model.

Musings about regulation by T-suppressors: a response to the commentary by Kristofor Ellestad on 'Meanderings into the regulation of effector class by the immune system: derivation of the trauma model'.

Any discussion of the regulation of effector class must include feedback control on the magnitude of the response. The induced effector activities are biodestructive and ridding. They are, in and of themselves, unspecific with respect to self and nonself. Consequently all responses include some level of innocent bystander pathology. The regulation of magnitude is essential to keeping this level of pathology at an evolutionarily acceptable level. This is my postulated role of suppressor T-cells, more popularly referred to as Treg. In order to perform this function they must be somatically selected to be anti-nonself like all other T/B-cells. If correct, any role that they might play in determining normal tolerance is excluded. As the commentary of Ellestad illustrates, their function to regulate autoimmunity is the consensus view today and, therefore, this competing concept and my analysis of suggested papers should invite a wide ranging debate.

Induction of lambda 1-immunoglobulin is determined by a regulatory gene (r lambda 1) linked (or identical) to the structural (c lambda 1) gene.

The cis-acting gene regulating specifically the inducibility of lambda 1-bearing B cells has been mapped within 2.9 cM of the structural gene. If the lambda 1lo-phenotype is due to the gly leads to val interchange in C lambda 1, then an argument can be made that (a) the lambda 1lo-phenotype is due to inefficient induction of lambda 1lo-bearing B cells and (b) B cell triggering is dependent upon a conformational change in the Ig receptor upon interaction with antigen. If the lambda 1lo-phenotype is due to a regulatory sequence linked to the structural C lambda 1-gene, then it must control the expression of the lambda 1-locus during development into adulthood, e.g., by an effect on methylation.

Determination of the kappa anti-alpha(1,3) dextran immune response difference by A gene(s) in the VKappa-locus of mice.

Mice lacking the V(alpha(1,3) (h gamma1)-gene do not produce a gamma1 anti-alpha(1,3) dextran response. However, on hyperimmunization some strains mount a kappa-anti-alpha(1,3) dextran response, whereas other remain nonresponder. Responsiveness in dominant. The kappa-anti-alpha(1,3) response difference is linked to the Ly-3 locus on chromosone 6 and is likely the result of a structural Vkappa-gene(s). In conjunction with previous work, three Vkappa-allogroups can now be distinguished. At present, this is the only example of an immune responsiveness difference associated with the Vkappa-locus.

On a regulatory gene controlling the expression of the murine lambda1 light chain.

We describe here two alleles, an allele of the lambda1 locus present in the SJL strain (rlambda1lo) and an allele of the lambda1 locus present in the BALB/c strain (rlambda1 +), of a regulatory gene locus which specifically influences the expression of the mouse lambda1 light chain structural gene. The rlambda1 regulatory gene is not linked to either the major histocompatibility complex or to the heavy-chain allogroup but appears to be linked to the lambda1 structural gene locus. In the homozygous state, the present of the rlambda1lo allele results in a 50-fold reduction in the number of lambda1 antigen-sensitive, bone-marrow derived lymphocytes (ASCs) compared to the presence of the rlambda1 + allele. However, those few lambda1ASCs present in rlambda1lo homozygotes can be induced normally to produce lambda1 light chains indistinguishable from those found in rlambda1 + homozygotes. The reduction in lambda1ASC's due to the rlambda1lo allele results both in a reduction in the amount of lambda1 Ig in the serum and also in a large variation in the magnitude of the lambda1 antibody response to alpha(1,3) dextran by individual animals. This variation permits the estimate that, on the average, 50 B cells of anti-alpha(1,3) specificity must be present per animal to permit a measurable response. Surprisingly, the expression of a gene locus regulating lambda1 light chain expression (rlambda1 locus) shows a clear gene dosage effect with rlambda1lo/rlambda1 + heterozygotes having 1/2 the number of lambda1ASCs and 1/2 the amount of serum lambda1 Ig as rlambda1 +/rlambda1 + homozygotes. This fact permits an analysis of the relationship between germ-line v-genes and their individual expression in serum Ig. The rlambda1 locus controls specifically a DNA-level event which occurs in stem cells as they become committed to lambda1 light chain expression. We postulate that the rlambda1 locus represents one of the DNA level recognition sites involved in the translocation event which places the vlambda1 and clambda1 structural genes in a transcriptional unit.

Functional characteristics of Peyer's patch lymphoid cells. II. Lipopolysaccharide is thymus dependent.

This study shows that LPS is not mitogenic in cultures containing B cells, or B cells and accessory adherent cells or ME, unless T cells are present. This observation rules out models of induction of antibody synthesis in which it is assumed that the delivery of a mitogenic signal by the interaction of LPS with the membrane of the B cell is in itself sufficient for B-cell induction (19). Further, it makes unlikely the proposed extrapolation of such a model to other so-called thymus-independent antigens, e.g., PVP, levan, dextran, and SIII (19). The mitogenic action of LPS appears to be due to its ability to complete an inductive stimulus to B cells (13). We interpret the observed thymus dependence of the B-cell response to LPS in light of a model in which two signals are obligatory for B-cell induction (14). The first signal in the inductive pathway is delivered to the antigen-sensitive cell via a conformational change in the receptor upon interaction with antigen. The second signal is delivered via the thymus-derived cooperating system. Since LPS can induce immune responses to both immunogenic and nonimmunogenic ligands (9-13) we envision that one signal is delivered to the B cell via specific binding of the ligand to the B-cell antigen receptor, while a second signal is delivered as a result of T-cell cooperation via membrane-bound LPS. This has been termed abnormal induction (20). In this example LPS is the foreign membrane-bound determinant in question although histocompatibility antigens (21, 22), viral determinants, or surface bound lectins could act similarly. In light of the above model, one observation should be pointed out. LPS inhibits the induction of a SRBC response in normal Peyer's patch cells to which adherent cells or ME is added. This inhibition appears to be a T-cell-mediated effect because it is abolished by partial depletion of the T-cell population by antitheta treatment. Since the induction of IgM producing PFC is being measured, the T-cell-dependent LPS inhibition could act either (a) by induction of T-cell "suppression" (23, 24) of the normal cooperating system required for a SRBC response, or (b) by the induction of such high levels of cooperating function (13) as to be inhibitory to a SRBC IgM response. Our observations contrast sharply with prior reports which describe LPS as a thymus-independent antigen (2-4) and a B-cell mitogen (5-8) capable of stimulating immune responses in the absence of T-cell cooperation (2-12). This demonstration of the thymus dependence of LPS stimulation has been possible because Peyer's patches from congenitally athymic (nude) mice are functionally a highly purified B-cell population devoid of T cells and accessory adherent cells. In this respect, earlier studies relied on nude spleen cultures and spleen cultures from thymectomized, lethally irradiated, and bone marrow-reconstituted mice (3, 4, 6-13). These spleen cultures which contain B cells and accessory adherent cells are recognized to be deficient but not devoid of the thymus-derived contribution to the inductive stimulus (12, 13). It could be argued that the presence of T cells and adherent cells is in fact required for the antigen-specific effect and not for the LPS effect. However, this is unlikely since our experiments show that LPS is not directly mitogenic for B cells and does not stimulate background anti-SRBC PFC. It seems unlikely that Peyer's patch antigen-sensitive cells differ from antigen-sensitive cells in the spleen in their mechanism of induction. We have shown that Peyer's patch B cells can be specifically induced by antigen, and Peyer's patch T cells mediate cooperating and killer functions. Alternately, the possibility that Peyer's patch B cells were not stimulated by LPS as a result of prior cryptic exposure to LPS (13) in the intestinal tract was excluded since cultures containing B cells, T cells, and adherent cells or ME were stimulated to DNA synthesis by LPS. The reason that certain antigens appear to be thymus independent may be that their repeating polymeric nature permits inductive interactions at very low levels of thymus-derived cooperation (see reference 20 for quantitative considerations). It has been stated that the inductive properties of all thymus-independent antigens are directly related to their ability to act as B-cell mitogens (19). The observation that LPS is thymus dependent for its B-cell mitogenic activity makes us question the thymus independence of any antigen.

The effect of 2-mercaptoethanol on murine mixed lymphocyte cultures.

Mouse spleen cells which have been depleted of adherent cells do not respond to allogeneic lymphocytes in vitro. Their cytotoxic response can be restored by inclusion of mercaptoethanol in the medium. Mercaptoethanol is shown to have a stimulatory effect also on the response of normal (unseparated) spleen cells to alloantigens. The enhancement of the DNA-synthetic and cytotoxic response is similar, varying from 3.5-15-fold. Cytotoxic cells also appear in unmixed lymphocyte cultures in the presence of mercaptoethanol and fetal calf serum. The specificity of these background cytotoxic cells is not known.

Tumorigenicity and lysis by natural killers.

Detailed analysis of the natural killer (NK) activity directed at nontumorigenic cell lines and their transformed tumorigenic derivatives has revealed a paradox. On the one hand, a correlation has been found between the tumorigenic potential of chemically transformed fibroblast cell lines and their sensitivity to NK cells in vitro. Nontransformed cells (N-type cell lines) and cells tumorigenic in normal mice (C-type cell lines) are resistant to NK-mediated lysis. In contrast, cell lines that are tumorigenic in ATxFL mice (these mice are very low in NK activity), but not in normal mice (I-type cell lines) are sensitive to NK-mediated lysis. These findings support the concept that NK activity is involved in host surveillance against tumors. On the other hand, NK-resistant fibroblasts, whether taken directly form animals or derived as tumorigenic or nontumorigenic cell lines, compete with NK-sensitive target cells to inhibit their lysis by NK effectors. Not only are both NK-sensitive and -resistant cells recognized by NK effectors but both receive lytic signals from NK effector cells. Target cell resistance is a result of a protein synthesis-dependent mechanism that prevents lysis such that in the presence of inhibitors of protein synthesis all fibroblasts tested are NK sensitive. Those fibroblasts that are normally sensitive to NK-mediated lysis must be deficient in their ability to produce or respond to this counterlytic mechanism. These findings are in contrast with the general findings when lymphoid cells are studied as NK targets where sensitivity appears to be a result of recognition by NK effectors. Because our findings show that transformed and normal cells express the same recognition determinants, in order for NK activity to play an important in vivo role in tumor surveillance, a mechanism must operate to permit NK effectors to find their targets in vivo. In the absence of a special discrimination mechanism, the killing of NK-sensitive transformants that arise autochronously would be less than optimal as a consequence of competition by the normal, NK-resistant, cells.

A new mouse immunoglobulin: IgG3.

A new subclass of mouse IgG for which we propose the name IgG3 has been shown to have a mol wt of 150,000 consistent with an L(2)H(2) structure, and is present in normal mouse serum at a concentration of 0.1-0.2 mg/ml. Its molecular weight, low carbohydrate content, glycopeptide analysis, and C-terminal analysis are all typical of the IgG class. The intact protein had a strong tendency to form noncovalent aggregates with itself which were dissociable in acid. Upon papain digestion an Fab fragment of 47,000 mole wt was generated along with an Fc fragment which was insoluble at neutral pH. As for its biology, the protein did not fix complement, was not cytophilic for gammaG2 receptor sites on macrophages, and did not show passive cutaneous anaphylaxis. It was very efficiently transported across the placenta so that its concentration in the newborn was twice that in the serum of the mother, compared to the concentration of IgG1 and IgG2 proteins which were only present at one-third the concentration of that found in the serum of the mother. The Fc fragment of this protein reacted with and was solubilized by the staphylococcal A protein which also precipitated the intact immunoglobulin. In addition, the myeloma protein which was the prototype for this gammaG subclass exhibited binding activity for levan which was localized to the Fab fragment.

The use of bacterial lipopolysaccharides to show that two signals are required for the induction of antibody synthesis.

Evidence is presented that antigen-sensitive cells require two signals for induction. Normally these two signals are delivered to the cell via the recognition of two determinants on the immunogen: the first the receptor on the antigen-sensitive cell, and the second by the cooperating cell system. The special experimental situation described here depends upon the observation that bacterial lipopolysaccharides (LPS) render immunogenic a variety of haptens. When monovalent haptens (TNP-amino acids) are added to spleen cultures, specific antihapten responses are induced in the presence of LPS. After analyzing competing interpretations of this phenomenon, we propose that the antigenic signal is delivered as the consequence of a conformational change in the receptor upon interacting with antigen, and the second signal is delivered directly via the interaction of LPS with the membrane on the antigen-sensitive cell receiving the antigenic signal, or indirectly via the interaction of LPS with the cooperating cell population. These data imply LPS is not itself a mitogen, but merely completes an inductive stimulus to B cells. The experimental results from these and other studies indicate how these two signals may participate in inductive, suppressive, and paralytic stimuli to antigen-sensitive cells.