The circumsporozoite protein (CSP) is the major surface protein of Plasmodium sporozoites, the infective stage of malaria. Although CSP has been extensively studied as a malaria vaccine candidate, little is known about its structure. Here, we show that CSP is proteolytically cleaved by a papain family cysteine protease of parasite origin. Our data suggest that the highly conserved region I, found just before the repeat region, contains the cleavage site. Cleavage occurs on the sporozoite surface when parasites contact target cells. Inhibitors of CSP processing inhibit cell invasion in vitro, and treatment of mice with E-64, a highly specific cysteine protease inhibitor, completely inhibits sporozoite infectivity in vivo.Malaria infection is initiated when an infected Anopheline mosquito injects sporozoites during a blood meal. After injection, sporozoites enter the bloodstream and go to the liver, where they invade hepatocytes and develop into exoerythrocytic forms. The circumsporozoite protein (CSP) is the major surface protein of the sporozoite and forms a dense coat on the parasite's surface. Studies have shown that CSP mediates sporozoite adhesion to target cells (for review see reference 1) and that it is required for sporozoite development in the mosquito (2). In addition, CSP has been extensively studied as a vaccine candidate and, thus far, is the only Plasmodium protein shown to confer protection to immunized individuals (for review see reference 1).Comparison of the deduced amino acid sequences of CS proteins from all species of Plasmodium shows that they have a similar overall structure (see Fig. 1 A and reference 1). They all contain a central repeat region whose amino acid sequence is species specific and two conserved regions: a five amino acid sequence called region I, immediately before the repeats, and a known cell-adhesive sequence with similarity to the type I thrombospondin repeat (TSR; reference 3). CSP has a canonical glycosylphosphatidyl inositol (GPI) anchor addition sequence in its COOH terminus; however, the presence of a GPI anchor has not been demonstrated.It was noted 20 yr ago that CSP immunoprecipitated from sporozoite lysates consists of one to two high MW bands (that differ by ‫ف‬ 1 kD) and a low MW band that is 8-10 kD smaller (4, 5). Biosynthetic studies showed that the initial label is incorporated into the top bands and the lower MW band appears later as a processed product (4, 5). The precise nature of this processing, as well as its functional significance, have remained unknown. In this report, we have determined the structural basis for this conserved feature of CSPs and have explored its role during sporozoite invasion of hepatocytes. RESULTS AND DISCUSSIONThe NH 2 -terminal portion of CSP is proteolytically cleaved by a cysteine protease To study the structure of the high and low MW CSP forms, we made polyclonal antisera to peptides representing the entire NH 2 -terminal and COOH-terminal thirds of CSP from Plasmodium berghei , a rodent malaria parasite. These antisera ...

In order to initially colonize a host, bacteria must avoid various components of the innate immune system, one of which is complement. The genus Bordetella includes three closely related species that differ in their ability to resist complement-mediated killing. Bordetella parapertussis and Bordetella bronchiseptica resist killing in naïve serum, a characteristic that may aid in efficient respiratory tract colonization and has been attributed to expression of O antigen. Bordetella pertussis lacks O antigen and is sensitive to naïve serum in vitro, yet it also efficiently colonizes the respiratory tract. Based on these observations, we hypothesized that B. pertussis may have an alternate mechanism to resist complement in vivo. While a number of reports on serum sensitivity of the bordetellae have been published, we show here that serum concentration and growth conditions can greatly alter the observed level of sensitivity to complement and that all but one strain of B. pertussis observed were sensitive to some level of naïve serum in vitro, particularly when there was excess complement. However, B. pertussis rapidly acquires increased resistance in vivo to naïve serum that is specific to the alternative pathway. Resistance is not efficiently acquired by B. parapertussis and B. bronchiseptica mutants lacking O antigen. This B. pertussis-specific mechanism of complement resistance does not appear to be dependent on either brkA or other genes expressed specifically in the Bvg ؉ phase. This in vivo acquisition of alternative pathway resistance suggests that there is a novel O antigen-independent method by which B. pertussis evades complement-mediated killing.

SUMMARYMonoclonal antibodies (mAbs) can discriminate phagocytes (mAb, RFD7+), antigen presenting cells (mAb, RFD1 +) and suppressor macrophages (mAbs, RFDI+RFD7+). Here we compare proportions of these subsets in normal mucosa and investigate changes associated with inflammatory disease. Biopsies were obtained from normal and inflamed lung, gut and skin. Cryostat sections were then analysed using mAbs RFD1 and RFD7. At normal mucosal surfaces the RFDI+RFD7 + suppressor cells consistently formed a major population: lung, RFD1 + 11.4%, RFD7 + 43.3%, RFDI+RFD7 + 45.2% and in gut, RFD1 + 37%, RFD7 + 12%, RFDI+RFD7 + 51% while in the skin the three subsets were in relatively equal "proportions (RFD1 + 30%, RFD7 + 37%, RFDI+RFD7 + 33%). In inflamed eczematous skin the percentage of RFDI+RFD7 + increased at the expense of RFD1 + and RFD7 + ceils whereas in inflamed mucosa the RFDI+RFD7 + population was significantly reduced (asthmatic lung 29%,

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