Juneann W. Murphy

Effects of Tumor Necrosis Factor Alpha on Dendritic Cell Accumulation in Lymph Nodes Draining the Immunization Site and the Impact on the Anticryptococcal Cell-Mediated Immune Response

ABSTRACT Cell-mediated immune (CMI) responses and tumor necrosis factor alpha (TNF-α) have been shown to be essential in acquired protection against Cryptococcus neoformans. Induction of a protective anticryptococcal CMI response includes increases in dendritic cells (DC) and activated CD4+ T cells in draining lymph nodes (DLN). During the expression phase, activated CD4+ T cells accumulate at a peripheral site where cryptococcal antigen is injected, resulting in a classical delayed-type hypersensitivity (DTH) reaction. Induction of a nonprotective anticryptococcal CMI response results in no significant increases in the numbers of DC or activated CD4+ T cells in DLN. This study focuses on examining the role of TNF-α in induction of protective and nonprotective anticryptococcal CMI responses. We found that neutralization of TNF-α at the time of immunization with the protective immunogen (i) reduces the numbers of Langerhans cells, myeloid and lymphoid DC, and activated CD4+ T cells in DLN and (ii) diminishes the total numbers of cells, the numbers of activated CD4+ T cells, and amount of gamma interferon at the DTH reaction site. Although TNF-α neutralization during induction of the nonprotective CMI response had little effect on cellular and cytokine parameters measured, it did cause a reduction in footpad swelling when mice received challenge in the footpad. Our findings show that TNF-α functions during induction of the protective CMI response by influencing the accumulation of all three DC subsets into DLN. Without antigen stimulated DC in DLN, activated CD4+ T cells are not induced and thus not available for the expression phase of the CMI response.

Natural Host Resistance Mechanisms against Systemic Mycotic Agents

The different fungi responsible for diseases in man are quite diverse in their characteristics. Some fungi are “true” pathogens in that they appear to infect normal individuals, whereas others are opportunistic and establish an infection only in an altered or compromised host. The natural portal of entry into the host varies among the fungi, but they usually fall within two major groups—those that enter by introduction into the skin, and those that enter through the respiratory route. The disease-causing fungi differ in their tissue preferences as well as in their morphological characteristics and size. These various features are important factors and must be considered in a discussion of the effectiveness of the natural host resistance mechanisms in eliminating the mycotic agents.

IN VITRO EFFECTS OF NATURAL KILLER (NK) CELLS ON CRYPTOCOCCUS NEOFORMANS

Publisher Summary This chapter examines the in vitro effects of natural killer cells on Cryptococcus neoformans (C. neoformans). In a series of experiments, NK cell reactivities of splenic cell populations were varied by nylon wool passage, varying donor mouse strains, using different aged mice, treating splenic cell donors with poly I:C or Corynebacterium parvum, and discontinuous Percoll gradient fractionation of the spleen cells. In each case, the NK reactivity of the effector cell pool was determined by using a 4 h 51Cr-release assay with YAC-1 targets with an effector:target ratio of 50:1, and the ability of the effector cells to inhibit the growth of cryptococci was measured by incubating C. neoformans isolate 184 with the effector cells at an E:T ratio of 500:1 for 18 h prior to enumerating the viable cryptococci by a plating technique. Although the numbers of C. neoformans cells increased in the assay vessels over the next 20 h, the % inhibition of cryptococci growth did not change significantly. It appears that the event that effects C. neoformans growth occurs relatively early in the incubation period and is detectable up to 24 h after mixing of effector and target cells.

NATURAL CELL-MEDIATED RESISTANCE IN CRYPTOCOCCOSIS

Publisher Summary This chapter examines natural cell-mediated resistance in cryptococcosis. In a study described in the chapter, BALB/c nude (nu/nu) and heterozygote (nu/+) mice were injected i.p. with 104 viable Cryptococcus neoformans (C. neoformans) cells seven days prior to collecting spleens, livers, lungs, and brains for determinations of the numbers of cyptococci colony forming units (CFU) per organ. Nude mice had fewer cryptococci in their tissues than did the heterozygotes. Because this difference appeared early after infection and because the lower CFU counts were in animals that could not mount a protective acquired immune response to C. neoformans, innate or natural mechanisms had to be functioning. The data presented in the chapter in conjunction with the data from in vitro experiments strongly suggest a role for natural killer (NK) cells or a subset of lymphocytes with similar characteristics and coexisting with NK cells in first line host resistance against C. neoformans. More work is required to determine the relative importance of the roles of these various natural cellular resistance mechanisms in cryptococcosis.