# Can immunocrit be used as a monitoring tool for swine vaccination and infection studies?

## TL;DR

This study evaluated if immunocrit can be used to monitor vaccination and infection in pigs, finding it not effective for tracking PCV-2 effects.

## Contribution

The study is the first to evaluate immunocrit as a monitoring tool for vaccination and infection in pigs.

## Key findings

- Immunocrit showed low to moderate correlation with other techniques like refractometry and γ-globulins.
- Immunocrit could not effectively monitor the effect of PCV-2 vaccination or infection.
- PCV-2 ELISA showed significant differences between vaccinated and non-vaccinated pigs after challenge.

## Abstract

The immunocrit is a cost-effective and straightforward technique traditionally used to assess passive immunity transfer to newborn piglets. However, it has not been previously used for monitoring the effect of vaccination and/or infections. Therefore, this study aimed to evaluate the usefulness of the immunocrit technique as an immunological monitoring tool in a vaccination and challenge scenario, using porcine circovirus 2 (PCV-2) as pathogen model. The immunocrit ratio was monitored in PCV-2 vaccinated (V) and non-vaccinated (NV) 3-week-old piglets (study day 0, SD0) that were subsequently challenged with this virus at SD21 and followed up to SD42. Additional techniques (PCV-2 IgG ELISA, optical refractometry, and proteinogram) were performed to further characterize the results of the immunocrit analysis.

Immunocrit, γ-globulin concentration and PCV-2 S/P values followed similar dynamics: descending after PCV-2 vaccination but ascending after an experimental PCV-2 inoculation. However, statistically significant differences between V and NV animals were only found with the PCV-2 ELISA. In this case, V animals had significantly higher (p < 0.05) S/P values (S/P ratio = 0.74) than NV (S/P ratio = 0.39) pigs only after challenge at SD42. On the other hand, serum total protein obtained by refractometer (STPr) were maintained from SD0 to SD21 and increased in both groups from SD21 to SD42. Correlations between techniques were low to moderate, being the most robust ones found between immunocrit and optical refractometry (ρ = 0.41) and immunocrit with γ-globulins (ρ = 0.39). In a subset of sera, the proteinogram technique was applied to the whole serum and the supernatant of the immunocrit, with the objective to characterize indirectly the immunocrit fraction. The latter one included all protein types detectable through the proteinogram, with percentages varying between 64.3% (γ-globulins) and 82% (β-globulins).

The immunocrit technique represented a fraction of the total serum proteins, with low to moderate correlation with all the complementary techniques measured in this study. Its determination at different time points did not allow monitoring the effect of vaccination and/or infection using PCV-2 as a pathogen model.

The online version contains supplementary material available at 10.1186/s40813-024-00380-y.