Histochemical study of calcium on T-tubule membranes and in the sarcoplasmic reticulum, in frog twitch muscle fibres at rest and during activity

The trigger calcium hypothesis of signal transmission between T-tubules and terminal cisternae (TC) of the sarcoplasmic reticulum (SR) in twitch muscle fibres implies the presence of calcium along T-tubule membranes at rest and its release upon excitation. To test this hypothesis, calcium was immobilised using a fixing and precipitating solution of glutaraldehyde in phosphate buffer at pH 8.0 and the calcium was substituted for by lead. Simultaneous tension recordings revealed the occurrence of contractions or a burst of twitches upon perfusion with the fixative. Procaine or tetrodotoxin (TTX) was used to inhibit this activity. In fibres without fixative-induced activity, precipitates were observed along T-tubules and in adjoining parts of TC. In activated fibres, tubular and TC precipitates were absent. These results are consistent with the trigger calcium hypothesis. In fibres activated by depolarisation, calcium returned to TC after passing successively through different parts of the SR.     

In vivo administration of Fab' fragments of anti-L3T4 (GK1.5) antibody inhibits the T helper cell function of murine lymph node cells

The effect of intravenous injection of Fab' fragments of anti-L3T4 antibody (GK1.5 monoclonal antibody) into mice was studied. This treatment depleted L3T4+ cells from the popliteal lymph nodes of keyhole-limpet hemocyanin-primed mice. The T cells that remained were unable to provide help to antigen-specific B cells in vitro. The results obtained using Fab' fragments were comparable with those using intact anti-L3T4 antibody and demonstrate that either form of GK1.5 is a potentially useful immunosuppressive agent in mice.     

Tumor dormancy. I. Regression of BCL1 tumor and induction of a dormant tumor state in mice chimeric at the major histocompatibility complex

The growth of the BCL1 tumor in murine H-2 chimeras was studied. Lethally x-irradiated BALB/c mice were reconstituted with C57BL/6 bone marrow that had been depleted of T cells. When chimerism was established 90 to 120 days later, large doses of BCL1 cells were injected. The tumor grew progressively, reaching a peak level of as many as 10(9) tumor cells per animal by 40 days after inoculation. After that time, the tumor regressed in all the chimeric animals, and by 100 days after inoculation, virtually all the animals appeared disease free as judged by an absence of BCL1-idiotype-positive cells in the spleen and peripheral blood, a normal spleen size, and absence of an elevated white blood cell count. Such animals were followed for as long as 8 mo after tumor inoculation and remained disease free. However, transfer of graded numbers of splenocytes from these animals into normal BALB/c recipients resulted in development of tumor in recipients receiving 100 or more spleen cells. These results indicate a large tumor burden in the spleen of each donor, namely, 10(6) to 10(7) BCL1 cells. The present model should facilitate characterization of the mechanisms underlying tumor dormancy.     

A B cell growth factor-like activity is secreted by cloned, neoplastic B cells

Supernatants from synchronized clones of neoplastic B cells (BCL1) were found to contain a B cell growth factor (BCGFI)-like activity. The BCGF activity in the BCL1 supernatants (SN) could synergize with EL-4 SN in the late phases of an IL 1-dependent BCGF I assay (days 5 through 8). These SN did not contain any detectable BCGF II, IL, 1, or IL 2 activity. In contrast to EL-4-derived BCGF I, which has a m.w. of approximately 18,000, the BCL1-BCGF activity has a m.w. of approximately 4500. Because the BCGF activity in BCL1 SN fluctuates with cell cycle in synchronized cultures, this BCL1-BCGF may play an auto-stimulatory role in B cell proliferation.     

Activation of antigen-enriched B cells. II. Role of linked recognition in B cell proliferation to thymus-dependent antigens

The responsiveness to T-dependent (TD) and T-independent (TI) TNP-antigens of murine splenic B cells previously enriched for antigen-binding cells (ABC) was examined. TNP-TI antigens induced B cell proliferation. TNP-TD antigens did not induce a proliferative response regardless of the physical form or nature of the TNP-TD antigen (e.g., soluble vs particulate, low or high haptenation of carrier, TNP on various insoluble matrices, etc.). TNP-TD antigens were effective in enhancing the response of the TNP-ABC to all concentrations of lipopolysaccharide (LPS) tested, indicating that binding of antigen to surface immunoglobulin alters the LPS responsiveness of the cell. Irradiated, keyhole limpet hemocyanin- (KLH) primed T cells induced a threefold to fourfold greater B cell proliferative response with TNP-KLH than with fluoresceinated KLH (FLU-KLH) or FLU-KLH together with TNP-human serum albumin (TNP-HSA). Therefore, linked recognition appears essential for optimal T cell-mediated B cell proliferation, whereas the induction of B cell proliferation via nonlinked, carrier-activated T cells is a minor component of the response.     

Kinetics of functional and morphological changes during decoupling and recoupling induced by glycerol in isolated muscle fibres of the crayfish

Summary The development of ultrastructural changes in the T-system of isolated muscle fibres of the crayfish by the glycerol procedure is described in correlation with the dissociation of excitation-contraction (E-C) coupling as well as with recoupling of the E-C link. The sequence of events in the process of disconnection of the tubules is as follows: dilation of the T-system tubules, disconnection of the constricted tubular segments from the surface membrane and from the T-system vesicle, disappearance of the lumen and its disintegration. The decoupled state is characterised by the presence of round vesicles uniformly distributed in the entire volume of the fibre. The volume of vesicles accounts well for the residual postglycerol volume increase (15%) of the muscle fibres. Functional and structural recovery can be induced by reapplication of glycerol to fibres decoupled and vesiculated with concentrations of glycerol300mmol · l^-1 in crayfish saline. The restitution starts with the organisation of the material of the disintegrated connecting segment of the T-system tubule into small vesicles which coalesce to form the tubule from the vesicular site. At the same time the surface membrane is invaginated toward the vesicle, thus forming the tubule from the surface membrane site. Recovery starts already in the first minute after application of glycerol and is completed within approximately 15min.     

Structural studies on the murine Ia alloantigens. VI. Evidence that both subunits of the I-A alloantigen are encoded by the I-A subregion.

The alpha and beta subunits of the murine I-A alloantigens from several H-2 haplotypes were examined by comparative tryptic peptide mapping by using double label (3H and 14C) techniques. Significant structural variation between alleles was detected in both subunits. Tryptic digests of the alpha polypeptides from s, b, and d showed only 65% co-elution with k; beta-chains from s, b, d, and r were about 50% similar to the k beta subunit. Peptide analysis of the Ak subunits from intra-H-2 recombinant strains indicated that both the alpha and beta polypeptides are encoded within the I-A subregion.     

An immunologic approach for the detection of tumor cells in the peripheral blood of patients with malignant lymphoma; implications for the diagnosis of minimal disease.

Lymphocytes were isolated from infiltrated lymph nodes and blood of eight patients with malignant lymphocytic lymphoma. All patients had normal numbers of circulating lymphocytes with normal morphology. None of the patients had serum paraproteins. The isolated lymphocytes from patients and controls were stained with affinity purified antibody specific for kappa- or lambda-light chains and analyzed by using a fluorescence activated cell sorter. Cells from infiltrated nodes stained for only one light chain type at high levels of fluorescence intensity. An increase in the number of brightly stained cells bearing the light chain type found in the involved node was readily detected in the peripheral blood of all but one of the patients with lymphoma. Similar changes in the ratio of kappa+- to lambda+-cells were not observed in 41 samples from nomral individuals and patients with other diseases.     

Inactivation of antigen-responsive clones with antisera specific for IgM or IgD.

The present study examines the isotype of cell surface immunoglobulins involved in triggering a response to thymus-dependent and thymus-independent antigens. Antibodies to immunoglobulin isotypes were used to block the in vitro interaction of receptor IgD and IgM with antigen. The results indicate that both IgD and IgM are necessary to trigger a response to TNP-SRBC but that only IgM is required for responsiveness to TNP-Brucella. Limiting dilution studies indicate that the inhibition of the immune response by antibody occurs at the level of precursor activation and suggest that there is no effect of antibody on subsequent proliferation of the daughter cells.