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Biomedical subjects

I Lefkovits

Publications and source records attributed to I Lefkovits.

At least 91 records · Page 5Linked to original sources
PubMed1977

Derivation of hybrids between a thymoma line and spleen cells activated in a mixed leukocyte reaction.

We have established 16 independent hybrid lines derived from a fusion between an AKR thymoma and mixed leukocyte reaction-stimulated C57BL/6 spleen cells. The hybrids express both parental H-2 alleles and show hybrid glucose-6-phosphate isomerase activity. Two of the lines showed Fc receptor activity not expressed in the parental thymoma. The AKR Thy-1.1 allele was expressed in all hybrid lines, but no Thy-1.2 could be detected. No killing activity was retained in the hybrid cells, probably because Sendai virus-mediated fusion of killer cells resulted in the lysis of the thymoma fusion partner.

Animals↗
PubMed1977

A method for autoradiographic studies of single clones of plaque forming cells.

By limiting dilution of B lymphocytes from spleens of immunized mice, microcultures were obtained that contained only one clone of plaque forming cells (PFC). The cultured cells were labelled with [14C]thymidine for varying periods of time. Plaques were obtained in monolayers of sheep erythrocytes in plastic dishes. After fixation with glutaraldehyde, the bottoms of the dishes were stripped off and autoradiograms prepared. By this method, it is possible to determine the proportion of labelled PFC within a given clone and to quantitate the incorporation of label. The method described can be applied to study the incorporation of other labelled molecules and for cytochemical investigations.

Animals↗
PubMed1977

Heterogeneity of B cells reacting with T-cell factors. Evidence for matching T-cell and B-cell subsets.

Spleen T cells have been stimulated with Concanavalin A (Con A) under conditions which lead to the production of non-specific factor (NSF), a substance which replaces T cells for B-cell responses to certain antigens. We have examined the ability of multiple aliquots of B cells to react to the NSF derived from single T cells, and have found great heterogeneity of response. We postulate that there exist subsets of T cells which vary in either the quantity or the quality of the non-specific factor(s) they can produce on stimulation, and that in turn there must also be matching subsets of B cells which may vary in their susceptibility to such factors.

Animals↗
PubMed1977

Antibody formation by human tonsil cells in vitro.

The ability of human tonsil lymphocytes to give an anti-SRBC response in conventional cultures and in microcultures was studied. It was found that about two-thirds of tonsils responded with a significant number of plaque-forming cells (PFC), and that in some instances the response could be augmented if allogeneic tonsil cell (irradiated or intact) were added. Moreover, tonsil lymphocytes which failed to give a response on their own often responded upon addition of an appropriate number of allogeneic tonsil cells. The response was remarkably improved if allogeneic tonsil supernatant or conditioned medium were added. An anti-SRBC response was also obtained if SRBC was omitted from the cultures. The frequency of anti-SRBC specific B cells was estimated as 1/60000 (f = 1-7 X 10(-5)).

Antibodies↗
PubMed1976

Effect of recent antigen priming on adoptive immune responses. IV. Antigen-induced selective recruitment of recirculating lymphocytes to the spleen demonstrable with a microculture system.

When thoracic duct lymphocytes (TDL) from mice given sheep erythrocytes (SRC) 1 day previously (1-day-primed TDL) were placed in microcultures with antigen for 5-6 days, the cells failed to produce antibody to SRC, but responded well to horse erythrocytes (HRC); reciprocal results were obtained with TDL from HRC-injected mice. The specific unresponsiveness of the TDL was observed despite the presence of an allogeneic factor in the cultures; this factor exerted not only a macrophage-like effect (TDL from normal mice failed to respond in the absence of this factor) but also a T-cell-replacing function. It was concluded therefore that the unresponsiveness of the TDL was the result of selective recruitment of specific B lymphocyte precursors from the recirculating lymphocyte pool to the lymphoid tissues; whether there was also recruitment of specific T lymphocytes was not investigated. Since addition of 1-day-primed TDL to cultures of normal TDL did not inhibit the response of the latter, there was no evidence that active suppression accounted for the unresponsiveness. The spleen appeared to be the main site for recruitment since 1-day-primed spleen cells placed in microcultures contained above normal numbers of specifically-reactive precursors. This was in striking contrast to the effect of transferring 1-day-primed spleen cells in vivo where, as previously reported, the cells fail to respond to the injected antigen within 1 wk of transfer. An explanation for this paradox is discussed.

Animals↗
PubMed1976

Antibody response of rabbit blood lymphocytes in vitro. Kinetics, clone size, and clonotype analysis in response to streptococcal group polysaccharide antigens.

Peripheral blood lymphocytes (PBL) of rabbits previously hyperimmunized against streptococcal groups A and A-variant antigens were stimulated in vitro by the corresponding vaccines to produce group-specific antibody. This response was dependent on an optimal cell density (2 X 10(6) cells/ml), on the presence of antigen, it was specific and cross-reactive due to a shared rhamnose backbone of the two polysaccharide antigens, and it was highly selective, such that in a 42-55-day culture 1 out of 20 viable cells was a specific PFC. During the exponential increase of the antibody concentration at a constant number of PFC, antibodies were secreted at a rate of 2.4 X 10(4) molecules/s per cell until a plateau level of antibody (40 mug/culture) was reached. The microculture system was used to determine the minimal frequency of group polysaccharide-specific precursor cells in the blood. Independent of the time elapsed since the last immunization this frequency was 1-3 X 10(-5), i.e., in the range of 1-2.8 X 10(2) precursor cells per ml blood. This number was further used together with the clonotype analysis of the culture supernates to calculate the frequencies of precursors of major and minor clonotypes. A hierachy of persisting clonal memory precursor cells was found indicating that clonal dominance is determined by locked-in frequency patterns and therefore it is a phenomenon based on numbers of cells that respond to the antigen.

Animals↗
PubMed1976

Limiting dilution analysis of helper T-cell function. II. An approach to the study of the function of single helper T cells.

Procedures have been described which are suitable for experiments utilizing a microculture system whereby one can easily study the function of single helper T cells. These are: (a) the elimination of the background anti-hapten response by preliminary anti-theta + guinea-pig complement complement treatment of the 'hapten-primed' population; (b) the removal of any contaminating hapten-specific B cells from the carrier-primed population by passage through nylon wool; (c) irradiation of long-term primed 'nylon wool' enriched helper cells tp prevent cell division; (d) the partition of individual helper cells by limiting dilution.

Animals↗
PubMed1976

Restriction in the function of single helper T cells.

T cells involved in specific and nonspecific co-operation belong to a long-lived population. However, under conditions of limiting dilution of T cells it is not a common event to detect both types of co-operative event in a single microculture well. Likewise, as far as specific co-operation is concerned, the simultaneous expression of both direct and indirect PFC responses in a single microculture well is also unusual. Estimates obtained of the number of PFC generated by one T cell in specific co-operation correspond well to those generated by a single B cell; and it would seem that under conditions of the microculture system there is a marked restriction in the number of B cells that a single T cell may interact with in the short term. This restriction seems to be of a one T-cell to one B-cell relationship.

Animals↗
PubMed1975

Antibody response to phosphorylcholine in vitro. I. Studies on the frequency of precursor cells, average clone size and cellular cooperation.

The anti-phosphorylcholine (PC) antibodies synthesized by BALB/c spleen cells in microcultures upon immunization with heat-killed vaccine of Pneumococci R36A (Pn) are directed exclusively to the PC epitope. These antibodies are of very restricted avidity and 88% of the responding clones express the idiotype characteristic of the TEPC-15 PC-binding myeloma. This idiotypic restriction appears to be due to the absence of clones capable of expressing other idiotypes, rather than to "clonal dominance". The estimated frequency of precursor cells for the PC epitope is 1 X 10(-5) to 2.5 X 10(-5). These precursors give rise to clones with an average size of 9 plaque-forming cells. When the logarithm of the number of negative wells was plotted against the number of spleen cells/well, the fraction of nonresponding cultures decreased exponentially as the number of spleen cells was increased. This indicated that only one cell type was limiting in our assay, presumably a B cell. Furthermore, treatment of spleen cells with AKR anti serum completely abolished the response to sheep red cells without affecting the response to PC. It is concluded that PC is a T cell-independent antigen. Of interest was the finding that PC requires adherent (A) cells and this is a particular characteristic of PC, since most T cell-independent antigens have been found not to require A cells. Reasons for the possible homogeneity of the response to PC are also discussed.

Animals↗
PubMed1975

Limiting dilution analysis of helper T-cell function.

Limiting dilution analysis has been applied to the study of T-cell 'helper' function in vitro. Using the microculture system one can estimate the numbers of (a) 'helper' T cells involved in specific collaboration with B cells and (b) those T cells which are able, on being activated by their specific antigen, to facilitate the response of B cells to another antigen. Such studies have enabled us to demonstrate that: (1) a single 'helper' T cell was able to activate a single B-cell precursor to detectable antibody production; (2) the 'helper' function of primed T cells was radio-resistant; (3) a minimal estimate of 'helper' frequencies could be obtained in defined cell populations; (4) nonspecific facilitation was directed towards virtually all available B cells of a given specificity if these were challenged with their appropriate particulate antigen; (5) the microculture system offers the opportunity to determine whether specific and non-specific T-cell 'helper' effects are a consequence of the activity of one T-cell type or of differenct subpopulations of T cells.

Animals↗
PubMed1975

T cell-dependent mediator and B-cell clones.

Supernatants were collected from keyhole limpet haemocyanin (KLH) primed spleen cells which had been incubated in tissue culture medium with their priming antigen KLH. These non-specific factor (NSF) containing supernatants were then tested in a microculture system for their ability to facilitate an anti-SRBC response of nu/nu or AT times BM spleen cells. It was concluded that:(a) NSF was able to engage a large number of the available pool of sheep erythrocyte (SRBC) specific B cells into an antibody response (b) this response was characterized by the development of clones expressing plaque-forming cells (PFC), the number of PFC produced within a clone being dependent upon the amount of NSF available in that culture; (c) NSF probably acted directly on B cells, and not via other accessory cell types.

Adjuvants, Immunologic↗