The subcutaneous movements of filarial infective larvae are impaired in vaccinated hosts in comparison to primary infected hosts

Abstract

Our aim in this study was to observe the movements of filarial infective larvae following inoculation into the mammalian host and to assess the effect of vaccination on larval migration, in situ. Here we present recordings of larvae progressing through the subcutaneous tissues and inguinal lymph node of primary infected or vaccinated mice. We used the filaria Litomosoides sigmodontis in BALB/c mice that were necropsied 6 hours after the challenge inoculation of 200 larvae. Subcutaneous tissue sections were taken from the inoculation site and larvae were filmed in order to quantify their movements. Our analyses showed that the subcutaneous larvae were less motile in the vaccinated mice than in primary-infected mice and had more leucocytes attached to the cuticle. We propose that this reduced motility may result in the failure of a majority of larvae to evade the inflammatory reaction, thereby being a possible mechanism involved in the early vaccine-induced protection.

Figure 1

A depiction of the subcutaneous tissue of mice inoculated with L. sigmodontis observed 6 hours post challenge: thin tissue section mounted in RPMI 1640, with dispersed infective larvae (asterisks, or arrowhead if damaged by the razorblade), a few nerves and adipose cells (dotted area) are present.

Figure 2

Assessements of the motility of infective larvae. The movements were assessed on recordings made of larvae in the subcutaneous tissue of vaccinated (Vacc) or primary infected (PI) mice and were scored on a discrete scale from 0 (non-motile) to 5 (maximum motility seen in larvae released in media only).