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Biomedical subjects

M C Lamers

Publications and source records attributed to M C Lamers.

At least 37 records · Page 2Linked to original sources
PubMed1991

Receptor-mediated elimination of phosphocholine-specific B cells in x-linked immune-deficient mice.

The combined expression of the M167 mu/kappa anstiphosphocholine (PC) transgenes with the x-linked immunodeficiency gene, xid, results in an almost total failure to develop B cells in the peripheral lymphoid organs of such mice. Although there is no significant difference between the normal transgene positive (TG+) female offspring and the immunodeficient TG+ xid males with respect to the number of B220+ pre-B cells and IgM+B220+B cells that develop in their bone marrow, the hemizygous xid males have 85% fewer B cells in their spleens than the phenotypically normal heterozygous F1 females. In xid M167-mu-transgenic mice, PC-specific B cells also fail to develop in the spleen; however, numerous B cells bearing the mua+VH1(+)-transgene product associated with endogenous kappa L chains that do not give rise PC-specific antibodies are present. In the phenotypically normal TG+ (B6.CBA/N x mu 243-4)F1 female mice, PC-specific B cells represent almost 10% of the total B cell population, and these B cells express an M167-Id that has been produced by association of the VH1 transgene product with an endogenous V kappa 24L chain. B cells expressing the normally dominant T15-Id are not detectable in the spleens of these M167 mu-transgenic mice. Furthermore, M167-Id+ B cells are present at a fivefold lower level in the bone marrow of mu-TG+ normal mice than in their spleens. These data suggest that the PC-specific B cells that develop in TG+ xid mice are either clonally deleted via some "IgR-directed" mechanism or they fail to receive the appropriate signals to exit the bone marrow or to enter the peripheral lymphoid tissues. This hypothesis is supported by the finding that TNP-specific B cells develop normally and do not undergo clonal deletion in xid mice carrying the Sp6 mu/kappa anti-TNP transgenes.

Animals↗
PubMed1991

Expression and biological effects of high levels of serum IgE in epsilon heavy chain transgenic mice.

We have generated and examined transgenic mice carrying a rearranged immunoglobulin transgene coding for the heavy chain of an IgE antibody. These mice produce the secreted form of the recombinant epsilon heavy chain. Serum IgE levels were increased at least 100-fold over control values. Transgenic epsilon mRNA was detected in spleen and thymus, not in liver and heart. Transgenic epsilon production in vitro was slightly up-regulated by T cells, but not affected by interleukin 4 in vitro or Nippostrongylus infestation in vivo. The B cell and T cell compartments and antigen-specific IgE, IgG1 and IgM responses as well as the increase in endogenous IgE after Nippostrongylus infestation in transgenic mice were normal. These data indicate that the presence of high levels of transgenic IgE did not induce class-specific suppressive mechanisms. Transgenic IgE bound to Fc epsilon receptor type I and Fc epsilon receptor type II and mediated histamine release from mast cells in vitro and an allergic skin reaction in vivo. It inhibited an ovalbumin-specific skin reaction in ovalbumin-immunized transgenic mice only during the initial phases of the immune response. This result has a bearing on the feasibility of immune therapy of allergic diseases with substances that block binding of IgE to its receptors.

Age Factors↗
PubMed1989

Elimination of CD8+ thymocytes in transgenic mice expressing an anti-Lyt2.2 immunoglobulin heavy chain gene.

Individual T cell populations are characterized by specific surface proteins, namely by the T cell receptor complex (TCR) and by two accessory molecules, CD8 (Lyt2) and CD4 (L3T4). CD8 and CD4 are required for T cell interactions with class I or class II major histocompatibility complex molecules. In the thymus, immature CD8(-4)-TCR- cells differentiate, possibly via a short stage of CD8+4- thymocytes, into CD8+4+ TCR+ T cells and mature further into the main T cell populations, the CD8+4- TCR+ cytotoxic T lymphocytes and the CD4+8- TCR+ T helper cells. In order to analyse the differentiation steps involving CD8, we generated transgenic mice expressing mu heavy chain genes from an anti-Lyt2.2 hybridoma. Transgenic lines expressing either the complete (mu sm) or only the secreted mu protein (mu s) suffer from a severe depletion of their CD8+4+ thymocytes affecting also the mature CD8+4- and CD4+8- populations. The depletion is correlated to the expression of transgenic mu-chain proteins within thymocytes. This intrathymocyte expression of the mu chain prevents CD8-4- thymocytes from further differentiation, most probably via intracellular interactions between mu heavy chain and CD8 proteins. These results show that CD8 plays an important role during thymocyte maturation.

Animals↗
PubMed1989

Immune status of a mu, kappa transgenic mouse line. Deficient response to bacterially related antigens.

We have examined the immune repertoire and immune response of a mouse that carries transgenes for a mu heavy chain and kappa light chain. The expression of these genes is under the regulation of their own controlling elements. The transgenes are expressed early in ontogeny and are easily detectable from day 13 of gestation onwards. The pre-B cells seem to function normally as they generate IgM-secreting colonies at normal frequencies. Colonies show predominantly the transgenic specificity. Expression of the transgenes is not limited to B cells since around 10%-20% of peripheral T cells and 50% of thymocytes express the mu transgene as an intracellular protein. Ectopic expression of kappa was not seen. The spleen size of the transgenic mouse is decreased by around 20%; this reduction is largely caused by a reduction of the B cell pool. Almost all B cells express the transgenes, only 30% co-express endogenous heavy chain genes and all co-express endogenous light chain genes. Serum Ig levels for IgM and IgA were normal, 20% of the IgM consist of the transgenic product. Serum IgG levels were decreased. T cell functions (helper and cytotoxic) were normal. Immune responses to conventional antigens were impaired, especially in the early phases of the immune response, but after boosting they were virtually normal, except for IgG3 which remained low. Primary antibody responses to T cell-independent antigens of the class II type (bacterially related antigens) were absent, although precursor frequencies for these antigens were within the expected range. The significance of this finding, as it relates to allelic exclusion of Ig genes, is discussed.

Animals↗
PubMed1988

The molecular interactions with helper T cells which limit antigen-specific B cell differentiation.

Helper T (Th) cell-dependent activation requirements for 2,4,6-trinitrophenyl (TNP)-specific resting B cells obtained from mice transgenic for Sp-6 mu, kappa genes were analyzed. Carrier-specific T cell help required linked recognition of TNP carrier and was functionally restricted by the B cell major histocompatibility complex. However, histoincompatible T cell-B cell conjugates formed by bridging surface immunoglobulin and Th cell receptor for antigen (TcR) through TNP-conjugated anti-TcR antibodies resulted in the efficient differentiation of TNP-specific B cells. Thus, Th cell-dependent cognate recognition of B cells is not obligatory. Specific conjugate formation could be obviated by using unconjugated fragments of anti-TcR antibodies. If dimeric, these fragments supported the Th cell-dependent differentiation of co-cultured histoincompatible resting B cells. Unconjugated monomeric fragments were ineffective, demonstrating the necessity for TcR cross-linking. Resting B cells from Sp-6+ mice rendered TNP-conjugated monomeric fragments of anti-TcR antibodies effectively multivalent, thereby satisfying conditions for the activation of co-cultured Th cells. The results demonstrate that Th cells do not transduce activation signals through TcR recognition of B cell membrane-associated ligand which limit the induction of B cell differentiation. Cross-linking of TcR on Th cells is required, sufficient and can be induced through interaction with the antigen-specific B cell surface.

Animals↗
PubMed1985

Antigen-antibody complexes bound to B-lymphocyte Fc gamma receptors regulate B-lymphocyte differentiation.

We studied the effect of soluble antigen-antibody complexes on the responses of polyclonally activated murine B lymphocytes. For this, normal B lymphocytes were stimulated with rabbit F(ab')2 anti-mu and lymphokines. IgG complexes, particularly in antigen excess, inhibited the plaque-forming cell response (55-70%), while proliferation was unaffected. Maximal inhibition was obtained with small amounts (0.2-1.0 microgram/ml) of complexes. Neither antigen or antibody alone was inhibitory. Inhibition was mediated via binding of the IgG complexes to Fc gamma receptors of B lymphocytes: (1) neither T lymphocytes or adherent accessory cells were required; (2) IgM complexes did not inhibit; and (3) inhibition was not seen when monoclonal anti-Fc gamma receptor antibodies prevented binding of the IgG complexes to these receptors. Kinetic experiments showed that B lymphocytes are susceptible to this inhibitory signal for only a short time after stimulation. We conclude that IgG complexes bound to the Fc gamma receptors of B lymphocytes regulate B-lymphocyte differentiation.

Animals↗
PubMed1984

Hybridoma 2.4G2: dissociation of the B-lymphocyte-triggering activity from the monoclonal anti-Fc IgG receptor antibody.

Previously, we have reported that monoclonal antibody specific for mouse Fc IgG receptors (Fc gamma R) [purified by affinity chromatography using goat F(ab')2 anti-rat Ig linked to Sepharose from supernatants of hybridoma 2.4G2] can induce both proliferation and antibody secretion of normal B-lymphocytes in the absence of T-lymphocytes. The current studies have shown that the B-cell-triggering activity is associated with a substance produced by 2.4G2 which can be distinguished from the 2.4G2 antibody by several criteria: (1) different preparations of 2.4G2 antibody with identical binding capacity for Fc gamma R differ markedly in their ability to trigger B-lymphocytes; (2) the B-lymphocyte-triggering substance and the anti-Fc gamma R antibody can be separated using insolubilized monoclonal mouse anti-rat kappa-antibody columns; and (3) the B-lymphocyte-triggering substance has a mol. wt of less than 50,000, while the 2.4G2 antibody has a mol. wt of 160,000. The B-lymphocyte-triggering moiety produced by the 2.4G2 hybridoma may be a previously undescribed lymphokine.

Animals↗
PubMed1982

Phagocytosis and degradation of DNA-anti-DNA complexes by human phagocytes: influence of the antibody class.

DNA-anti-DNA complexes were prepared with igG anti-DNA or IgM anti-DNA and incubated with monocytes and neutrophils from human blood. The capacity of the complexes to induce phagocytosis and degradation of the antigen by the phagocytes varied with the composition of the complexes. Complexes prepared with IgG anti-DNA were readily processed (phagocytosed and degraded) by the cells, provided the complexes were large (precipitating at 3000 x g in 15 minutes). Processing of the complex required the Fc part of the IgG antibody. Complexes prepared with IgM anti-DNA were hardly processed at all, although they were as large as the IgG anti-DNA-containing complexes that were processed. IgM anti-DNA enhanced the processing of IgG anti-DNA-DNA complexes by increasing the size of the complexes.

Antigen-Antibody Complex↗
PubMed1981

Phagocytosis and degradation of DNA-anti-DNA complexes by human phagocytes. I. Assay conditions, quantitative aspects and differences between human blood monocytes and neutrophils.

The uptake in vitro was studied of 3H-labeled DNA-anti-DNA complexes by neutrophils and monocytes from human blood. Complexes were prepared from 3H-labeled circular double-stranded (dS) DNA of bacteriophage PM2 and anti-dsDNA-containing sera from patients with systemic lupus erythematosus. After phagocytosis, cells and medium were separated. The cells were treated with DNase to remove adherent and noningested complexes before the cell-associated radioactivity was counted. Thus, only complexes inside the cells were measured. The medium was analyzed for acid-precipitable radioactivity. In this way, we found that neutrophils only phagocytose the complexes, whereas monocytes phagocytose the complexes and degrade the antigen. In contrast, both types of phagocyte degraded the antigen in tetanus-anti-tetanus complexes. The degradation took place after phagocytosis, inside the cells. The difference in DNA degradation between neutrophils and monocytes correlated with the difference in acid DNase activity of the lysosomal fractions: monocytes contained DNase activity, neutrophils did not. With complexes made from DNA with 131I-labeled anti-DNA, we found that both cell types degraded the antibody. Uptake of complexes and degradation of antigen increased with incubation time and cell concentration and was saturable with respect to complex concentration. The processes were inhibited by 5 mM mono-iodoacetic acid or by low temperatures.

Antigen-Antibody Complex↗
PubMed1981

Phagocytosis and degradation of DNA-anti-DNA complexes by human phagocytes II. Influence of the size of the complexes.

The influence was studied of the size of DNA-anti-DNA complexes on their capacity to induce phagocytosis and degradation by monocytes and neutrophils from human blood. An estimate of the size of the complexes was obtained by precipitation analysis, sucrose-gradient velocity sedimentation and filtration over Nucleopore filters. The results show that only those complexes are processes that precipitate in 15 min at 3000 x g. These complexes have an S value of more than 25000 and a diameter of more than 0.4 micrometer. Likewise, tetanus-anti-tetanus complexes also had to be precipitable in 15 min at 3000 x g to be processed by the phagocytes.

Antigen-Antibody Complex↗
PubMed1980

Dissociation of DNA/anti-DNA complexes at high pH.

A high-avidity human antibody (Ab) to double-stranded DNA (dsDNA) could be virtually completely dissociated from Crithidia luciliae kinetoplast dsDNA at pH 12 and a low-avidity Ab at pH 11. At low pH (pH 2), no dissociation occurs of either Ab. Low-avidity Ab could be dissociated at neutral pH with 1 M NaCl, but even with 5 M NaCl high avidity Ab could not be dissociated. Prolonged exposure to pH 12 did not affect DNA-binding by Ab after dialysis against PBS. A decrease in surface tension of the liquid medium in no case prompted dissociation. Contact angle measurements on DNA showed it to be very hydrophilic. It is concluded that concomitant with the strong negative charge of the antigen and the positive charge of the Ab, both antigenic determinant and antibody-active site are exceptionally hydrophilic, which causes their van der Waals attraction in aqueous media to be negligibly small. This particular antigen-antibody bond thus is mainly electrostatic and can be completely dissociated by abolishing the positive charge of the antibody-active site through a drastic increase in pH.

Antibody Affinity↗
PubMedDate not supplied

In vivo analysis of the cytoplasmic domain of mIgE antibodies.

All immunoglobulin molecules exist in two forms, one integrated into the plasma membrane and displayed on the cell surface as the B cell receptor [1], the other secreted into tissue fluids as the soluble antibodies. Any given B lymphocyte has the potential of producing both forms. The membrane-bound form and the secreted form produced by a single B cell have identical light chains and identical heavy chains except for a short segment at the C terminus. This segment consists of a 'spacer' sequence, followed by a stretch of hydrophobic amino acids (transmembrane region) and the cytoplasmic region which differs in size between the Ig classes. Little is known about the function of intracellular tails of IgG, IgA and IgE. They differ from those of IgM and IgD, which have only three intracellular amino acids (Lys Val Lys). The intracellular parts of IgG, IgA and IgE are longer. Using a gene targeting technique by homologous recombination in ES cells [2, 3], combined with the prokaryotic CRE-recombinase system [4], we constructed two mice. One with the membrane exons and a mutated cytoplasmic tail in place (KVKdelta tail), and one with essentially only the sequence coding for the secreted form of IgE (delta M1M2). Measurements of the steady-state level of IgE showed that in delta M1M2 mice IgE can only be detected at a minimal level, whereas in KVKdelta tail mice serum IgE is reduced by about 50%. These data allow us to speculate about a specific function of the cytoplasmic tail of mIgE antibodies. We think that the cytoplasmic tail of IgE is involved in signal transduction which leads to the expression of high quantities of secreted IgE.

Animals↗