Protective activities of ribosomal ribonucleic acid and lipopolysaccharide of Pseudomonas aeruginosa: a comparative study

DDA as an immunological adjuvant

As compared to other adjuvants, DDA is a moderate or strong adjuvant for humoral responses and a strong adjuvant for CMI, especially DTH responses, against different types of antigens and in both laboratory animals and larger animals. DDA can collaborate with other immunomodulating compounds resulting in further enhanced responses. Mechanisms include interactions with both antigen and components of the host immune system and possibly, multiple beneficial effects contribute to the relatively strong adjuvanticity of DDA. Toxicity of DDA is not known but severe detrimental side effects were not seen. This adjuvant can be applied in experimental vaccines and in commercial vaccines for veterinary purposes, especially if cell-mediated immunity is considered to be important. In immunology, DDA can be of use to study T helper cells responsible for DTH responses (T helper cells type 1) and to characterize T helper cell epitopes on antigens (Snijder et al., 1992).

Antibacterial resistance, macrophage influx, and activation induced by bacterial rRNA with dimethyldioctadecylammonium bromide

Intraperitoneally injected rRNA from Pseudomonas aeruginosa combined with dimethyldioctadecylammonium bromide (DDA) increased nonspecifically the resistance of mice against an intraperitoneal challenge with extracellular (P. aeruginosa, Escherichia coli) and intracellular (Listeria monocytogenes) bacteria. This study concerns the mechanism underlying the nonspecific resistance. RNA with DDA (RNA-DDA) induced a cell influx and activated peritoneal macrophages (M phi) as judged by the decreased 5'-nucleotidase and alkaline phosphodiesterase activities in M phi lysates, the enhanced O2- release, and the increased antitumor activity in comparison with unstimulated M phi. RNA without DDA did not enhance the resistance and did not influence the peritoneal cell numbers or M phi properties. DDA without RNA enhanced the resistance of mice only slightly; it induced a cell influx, yielding elicited M phi as judged by the decreased 5'-nucleotidase activity and increased alkaline phosphodiesterase activity, the slightly enhanced O2- release, and the absence of increased antitumor activity. Both RNA-DDA and DDA M phi showed an enhanced capacity to ingest and kill L. monocytogenes in vitro, DDA M phi being slightly less effective than RNA-DDA M phi with respect to killing. We conclude that the enhanced killing capacity of M phi for L. monocytogenes is characteristic of both elicited DDA M phi and activated RNA-DDA M phi. The relationship between nonspecific resistance, peritoneal cell numbers, and antibacterial M phi activity is discussed. In addition, it is shown that RNA and DDA retain their activity when they are injected apart, suggesting that they activate M phi by sequential action.

RNase-sensitive and RNase-insensitive protective components isolated from Listeria monocytogenes

Crude ribosomes were isolated from Listeria monocytogenes serotype 4b and separated into two fractions by molecular sieve chromatography. Chemical analysis indicated that fraction I contained cell envelope components while fraction II contained the ribosomes. Both fractions protected mice against Listeria, but only in combination with the adjuvant dimethyldioctadecylammonium bromide (DDA). RNase-treatment, but not proteinase K-treatment destroyed the protective properties of fraction II, and RNA purified from fraction II also induced protection. Protection induced by fraction I was not affected by either RNase- or proteinase K-treatment. Both subcutaneous and intraperitoneal, but not intravenous administration of fraction I, fraction II, or purified RNA induced significant protection against intraperitoneal infection, the intraperitoneal route of administration being the most effective. All preparations induced high levels of protection 3 to 7 days after administration, but protection was already decreased after 14 days. Protection induced with RNA appeared to be biphasic, because it also protected mice 1 day, but not 2 days after administration. Protection induced with both fraction I and RNA was at least in part non-specific, because both preparations also protected mice against L. monocytogenes serotype 3, Streptococcus pneumoniae and Pseudomonas aeruginosa. Results are discussed in relation to previous work with analogous preparations from P. aeruginosa.

Ribonuclease-sensitive ribosomal vaccines

This paper presents an analysis of the protective properties of the components in ribonuclease (RNase)-sensitive ribosomal vaccines, in particular the ribonucleic acid (RNA). The protective activities in mice of purified ribosomes derived from Pseudomonas aeruginosa and from Listeria monocytogenes were compared. Both ribosomal vaccines had to be combined with the adjuvant dimethyldioctadecylammonium bromide (DDA) in order to be protective, and both lost their activity after RNase treatment. The ribosomal vaccines as well as RNA purified from the ribosomes induced non-specific protection. Intraperitoneal injection of RNA with DDA induced an influx of peritoneal cells. Furthermore, RNA with DDA activated macrophages as shown by, a.o., enhanced phagocytic activity and killing capacity for L. monocytogenes. The results suggest that the observed macrophage activation is probably T-cell-independent. With regard to the ribosomal vaccine of P. aeruginosa it is concluded that RNA also contributed to the protective activity by increasing the humoral response against suboptimal concentrations of contaminating cell surface antigens. In conclusion, it is proposed that ribosomal vaccines may be considered as a combination of a non-specific immunomodulator (RNA) with pathogen-specific cell surface antigens. This concept of ribosomal vaccines is discussed in relation to the literature concerning RNase-sensitive ribosomal vaccines.