Question 6

Immunologists investigated the immune responses of healthy guinea pigs and guinea pigs with contact hypersensitivity (sensitised to the chemical allergen Phthalate-Y, or PY).

PY triggers an allergic skin reaction in sensitised guinea pigs, causing local tissue swelling. The researchers applied a solvent vehicle (liquid paraffin) alone to the left ear of each guinea pig, and PY dissolved in liquid paraffin to the right ear.

The immune response was evaluated using two markers:

the cellular response, by measuring the mean increase in ear thickness (in $μm\mu\text{m}$ ) 48 hours after application
the humoral response, by measuring the mean serum concentration of anti-PY IgG antibodies (in arbitrary units) 14 days after application.

Table 1 shows the findings of this study. The values in brackets represent $\pm 2\,$ standard deviations (SD). A range of $\pm 2\,$ standard deviations from the mean captures approximately 95% of the data.

Table 1

Type of guinea pigs	Sex of guinea pigs	Mean increase in ear thickness / $μm\mu\text{m}$	Mean concentration of anti-PY antibody / arbitrary units
Healthy control	Male	$(±1.8)12.4\ (\pm 1.8)$	$(±1.2)8.5\ (\pm 1.2)$
Healthy control	Female	$(±1.5)11.2\ (\pm 1.5)$	$(±1.0)9.0\ (\pm 1.0)$
Sensitised	Male	$(±3.1)22.5\ (\pm 3.1)$	$(±1.5)10.2\ (\pm 1.5)$
Sensitised	Female	$(±1.6)13.1\ (\pm 1.6)$	$(±4.2)21.4\ (\pm 4.2)$

Suggest and explain one reason why the liquid paraffin vehicle on its own was applied to the left ear of the guinea pigs.

What can you conclude about the effects of contact sensitisation on the cellular response and the humoral response in male and female guinea pigs? Use the data in Table 1 to justify your conclusions.