Modifications in a French pressure cell-laboratory press system

Enzymatic activities of human cytomegalovirus maturational protease assemblin and its precursor (pPR, pUL80a) are comparable: [corrected] maximal activity of pPR requires self-interaction through its scaffolding domain

Herpesviruses encode an essential, maturational serine protease whose catalytic domain, assemblin (28 kDa), is released by self-cleavage from a 74-kDa precursor (pPR, pUL80a). Although there is considerable information about the structure and enzymatic characteristics of assemblin, a potential pharmacologic target, comparatively little is known about these features of the precursor. To begin studying pPR, we introduced five point mutations that stabilize it against self-cleavage at its internal (I), cryptic (C), release (R), and maturational (M) sites and at a newly discovered "tail" (T) site. The resulting mutants, called ICRM-pPR and ICRMT-pPR, were expressed in bacteria, denatured in urea, purified by immobilized metal affinity chromatography, and renatured by a two-step dialysis procedure and by a new method of sedimentation into glycerol gradients. The enzymatic activities of the pPR mutants were indistinguishable from that of IC-assemblin prepared in parallel for comparison, as determined by using a fluorogenic peptide cleavage assay, and approximated rates previously reported for purified assemblin. The percentage of active enzyme in the preparations was also comparable, as determined by using a covalent-binding suicide substrate. An unexpected finding was that, in the absence of the kosmotrope Na2SO4, optimal activity of pPR requires interaction through its scaffolding domain. We conclude that although the enzymatic activities of assemblin and its precursor are comparable, there may be differences in how their catalytic sites become fully activated.

Immune response modulation by colonization of germfree rats with Propionibacterium acnes

Propionibacterium acnes (oral and/or parenteral administration) had a modulating effect on antibody-and cell-mediated immune responses of germfree (GF) and monoassociated (MA) rats. In conventionally reared rodents, parenteral injection of killed P. acnes stimulated the splenic plaque-forming cell response to sheep erythrocytes. However, in GF rats and in rats monoassociated with viable P. acnes, parenteral injection of killed P. acnes antigen inhibited the plaque-forming cell response to sheep erythrocytes. When compared with the responses of GF control rats, splenocytes from GF rats parenterally injected with P. acnes antigen had a decreased in vitro blastogenic response to phytohemagglutinin and concanavalin A and an increased blastogenic response to homologous bacterial antigens. Conversely, a parenteral injection of P. acnes antigen into P. acnes MA rats resulted in an increased splenocyte blastogenic response to phytohemagglutinin and concanavalin A but not to homologous (P. acnes) antigens. Thus the presence or absence of intestinal antigenic stimuli (in MA and GF rats) had a modulating effect on the immune response to a parenteral injection of P. acnes antigen.

Effect of systemic candidiasis on blastogenesis of lymphocytes from germfree and conventional rats

Germfree and conventional rats were challenged (intravenously) with Candida albicans and sacrificed at various times after infection, and their spleen cells were harvested to examine the effect of disseminated candidiasis on in vitro lymphocyte hypersensitivity to Candida antigens (CA). Results showed that conventional rat splenocytes, initially responsive in vitro to stimulation by CA, manifested a depression in CA-specific responsiveness after challenge with viable C. albicans (days 3 to 6 postchallenge). In addition, the latter splenocyte response to phytohemagglutinin (PHA) and concanavalin A (ConA) was suppressed by 3 to 6 days after challenge with Candida. In contrast to conventional rats, the response of germfree rat splenocytes to CA was insignificant before challenge with C. albicans, and it was increased at 9 days after infection. The response of uninfected germfree rat splenocytes to PHA and ConA was significantly lower than that of unchallenged conventional rats. Challenge with viable C. albicans did not result in a suppression of gnotobiotic rat splenocyte responses to PHA and ConA, but rather, the disseminated infection resulted in as much as fivefold increases in PHA or ConA-induced blastogenesis. These findings suggest that disseminated candidiasis is capable of suppressing blastogenesis in immunologically mature conventional rats and of improving lymphocyte blastogenesis from immunologically immature germfree rats.

Immunity to Candida albicans induced by Listeria monocytogenes

Immunity to Candida albicans was studied in Swiss-Webster white female mice. Lethal and sublethal infections with C. albicans did not enhance immunity to a subsequent Listeria monocytogenes challenge. Mice sensitized to L. monocytogenes and then challenged with C. albicans intravenously were able to reduce the population of C. albicans in their kidneys after being boosted (rechallenged) with L. monocytogenes. However, the acquired cellular immunity so induced was very short-lived. Both C. albicans-sensitized and nonsensitized control mice showed an immediate-type and delayed-type skin test response to the cell wall antigen(s) of C. albicans but not to the cytoplasmic antigen(s). There did not appear to be any correlation between increase in skin test response and progression of the candida infection in mice.

Construction of a laboratory press for use with the French pressure cell

A motor-driven hydraulic press has been designed to overcome problems previously encountered with the use of the French pressure cell.