# An insight into the salivary gland content of the human body louse, Pediculus humanus

## TL;DR

This study explores the saliva composition of human body lice, revealing unique proteins and a complex gland system.

## Contribution

The first next-generation sequencing and proteomic analysis of the human body louse sialome.

## Key findings

- The majority of salivary gene products and proteins in body lice are not closely related to known biomolecules.
- Despite distinct gland morphology, there is a high overlap in salivary products between Bean- and U-shaped glands.
- The complex salivary gland system suggests strong evolutionary pressure to maintain both gland types.

## Abstract

Human body lice, Pediculus humanus humanus, are blood-feeding parasites that live in clothing and feed several times per day. Saliva injected during louse feeding induces pruritis and local inflammation in the skin. If untreated, chronic Pediculosis can cause systemic negative health effects. Despite the medical importance of body lice and their longstanding association with humans, characterization of their saliva has been limited. To address this, we extracted RNA and protein from two of the body louse’s morphologically distinct sets of salivary glands (Bean-shaped and U-shaped) and generated transcript and protein profiles for each. Additionally, we performed fluorescent staining and confocal microscopy on each gland type to enhance descriptions of their structure and gross cellular architecture. Analysis of body louse salivary gene products and proteins revealed that the overwhelming majority were not closely related to biomolecules of known function, highlighting the organism’s unique and understudied saliva composition. Despite the contrasting morphology of the two gland types, there was a high degree of overlap in the salivary products produced. This finding suggests strong Darwinian selection pressure to maintain both salivary gland types, given that it would be simpler to have a single morphologically identical set of glands. Here we present the first next-generation sequencing and proteomic characterization of the human body louse sialome, discuss the potential physiological importance of louse salivary proteins, and consider possible explanations for why lice have a complex salivary gland system despite inordinate redundancy in the protein repertoire of the Bean- and U-shaped salivary glands.