No abstract

Autoimmune-prone MRL/lpr mice, homozygous for the lpr mutation, exhibit defective apoptosis and develop generalized lymphoproliferation with the accumulation of a double-negative (DN: CD4- CD8-) T cell population. The capacity of lpr T lymphocytes to effectuate Fas- and perforin-mediated cytotoxicity was investigated. Spleen and lymph nodes cells spontaneously lyse Fas- targets (thymocytes) through a Fas-mediated mechanism as a consequence of their overexpression of Fas ligand (FasL) confirmed by semiquantitative reverse transcription (RT)-PCR and immunoprecipitation analysis. This cytotoxicity was greatly increased after stimulation of the effectors by phorbol myristate acetate (PMA) + ionomycin. Under these conditions, MRL/lpr spleen and LN cells exhibited strong Fas-mediated Ca2+-independent cytotoxic activity against wild-type Fas+ (H-2 compatible or incompatible) thymocytes or lipopolysaccharide (LPS)-transformed blast cells. Such Fas-mediated cytotoxic activity was also observed with C57BL/6-lpr, but never with wild-type C57BL/6 or MLR+/+ effectors. Depletion experiments showed that the effector cells of this Fas-mediated cytotoxicity were DN T cells. This subset, which represent in vivo activated T cells, can spontaneously lyse Fas+ targets by a mechanism that does not need the interaction of the T cell receptor (TCR) with major histocompatibility complex molecule plus antigen. This lytic potential is increased by PMA + ionomycin, which sends a second activation signal to these primed T cells. Therefore, the small amounts of Fas receptor expressed on MRL/lpr tissues may account for their nonspecific autoimmune attack by DN cells. In Con A-containing medium, which allows detection of the perforin-mediated pathway against Fas targets, cytotoxic CD8+ effectors were detected that are able to kill lpr thymocytes via a Ca2+-dependent pathway. Thus, in MRL/lpr mice, these CD8+ cells could constitute potent cytotoxic effectors against cells presenting antigen to their TCR.

Insulin receptors from C57BL16J mouse (II-2b) liver membranes were specifically labeled with i2%-photoreactive insulin by UV irradiation. Membranes were solubihzed and the capacity of various antibodies reading with the major histocompatibility complex to immunoprecipitate insulin receptors was tested.

LINE-1 are endogenous mobile genetic elements that have dispersed and accumulated in the genomes of eukaryotes via germline transposition, with up to 100 000 copies in mammalian genomes. LINE-1 elements transpose by reverse transcription of their own transcript. Transposition requires synthesis of a full-length, sense-strand transcripts and proteins encoded by open reading frame (ORF) 1 and ORF2. Although severely repressed in most normal tissues, LINE-1 occasionally leads to disease by insertional mutagenesis. In the present study, Northern blot and in situ hybridization analyses revealed a template-strand transcription of LINE-1 ORF2 (encoding reverse transcriptase, RT) in lymphoid organs and the liver from MRL-+/+ and Fas-deficient MRL/lpr strains and their normal ancestors. While these sense transcripts are restricted to the nucleus in hepatocytes, they are also found in the cytoplasm in splenocytes. In contrast to transcription, ORF2 translation was detected only in MRL strains, as shown by the cytoplasmic labelling of splenic cells obtained with a monoclonal antibody recognizing the LINE-1 RT. This antibody coprecipitated two proteins of 45 and 12 kDa from MRL/lpr lymphoid organ lysates that were removed by pretreatment with anti-b2-microglobulin antiserum, suggesting a structural association between a LINE-1 product and a major histocompatibility complex class I or class I-like molecule.

SUMMARY CBA/J (H‐2k) females, mated with DBA/2 J (H‐2d) or DBA/1 J (H‐2q) males, exhibit a high rate of fetal resorption. In contrast, when H‐2 identical CBA substrains (i.e. CBA/Ca and CBA/N) are used, this phenomenon is not observed. On the other hand, before mating with DBA/2 J males, pre‐immunization of CBA/J females with spleen cells coming from BALB/c J or (DBA/2 x BALB/c J) F1 males (and not from other H‐2d identical males whatever their Mls alleles) has significantly decreased the fetal resorption rate. Thus, immunization against determinants other than classical H‐2d (K, I, D, L) antigens (transmitted as a dominant character and different from Mls determinants) can elicit anti‐abortive effects. Furthermore, it was observed that the spleen cell endowed with the anti‐abortive effects was neither a T nor a B lymphocyte. In contrast, peritoneal cells were able to reproduce the phenomenon, indicating that it may be mediated by a cell of the macrophage‐monocyte lineage. Finally, a first gestation was substituted for allo‐immunization of CBA/J females. The anti‐abortive effects of a first pregnancy by BALB/c J males (and not by other H‐2k syngeneic or H‐2d allogeneic males) was observed in the course of a second pregnancy sired by DBA/2 J males. These data can be interpreted in terms of maternal recognition of an antigen present on both macrophages and trophoblast cells and necessary for a successful gestation, which is coded for by genes outside the K, I, D, L regions.